diff --git a/cmd/vellum/main.go b/cmd/vellum/main.go
index 62a5834..1ed253a 100644
--- a/cmd/vellum/main.go
+++ b/cmd/vellum/main.go
@@ -15,6 +15,7 @@ import (
 	"github.com/mithral/vellum/internal/auth"
 	"github.com/mithral/vellum/internal/core"
 	"github.com/mithral/vellum/internal/httpapi"
+	"github.com/mithral/vellum/internal/library"
 	"github.com/mithral/vellum/migrations"
 )
 
@@ -65,9 +66,12 @@ func run() error {
 		return fmt.Errorf("bootstrap admin: %w", err)
 	}
 
-	auth.NewHandlers(authenticator, log).Register(api.Mux())
+	authHandlers := auth.NewHandlers(authenticator, log)
+	authHandlers.Register(api.Mux())
 	api.SetAuth(authenticator)
 
+	library.NewHandlers(db, log, authenticator).Register(api.Mux())
+
 	srv := &http.Server{
 		Addr:    cfg.Listen,
 		Handler: api.Handler(),
diff --git a/internal/core/migrate_test.go b/internal/core/migrate_test.go
index e05911d..7045d32 100644
--- a/internal/core/migrate_test.go
+++ b/internal/core/migrate_test.go
@@ -43,8 +43,8 @@ func TestMigrateAppliesAndIsIdempotent(t *testing.T) {
 	if err := db.QueryRowContext(ctx, "PRAGMA user_version").Scan(&version); err != nil {
 		t.Fatalf("read user_version: %v", err)
 	}
-	if version != 1 {
-		t.Errorf("user_version = %d, want 1", version)
+	if version != 2 {
+		t.Errorf("user_version = %d, want 2", version)
 	}
 
 	var tables int
diff --git a/internal/library/handlers.go b/internal/library/handlers.go
new file mode 100644
index 0000000..267333a
--- /dev/null
+++ b/internal/library/handlers.go
@@ -0,0 +1,230 @@
+package library
+
+import (
+	"database/sql"
+	"errors"
+	"log/slog"
+	"net/http"
+	"strconv"
+
+	"github.com/mithral/vellum/internal/auth"
+	"github.com/mithral/vellum/internal/httpx"
+)
+
+// Handlers serves library management and scanning endpoints.
+type Handlers struct {
+	db   *sql.DB
+	log  *slog.Logger
+	auth *auth.Authenticator
+}
+
+// NewHandlers builds the library HTTP layer.
+func NewHandlers(db *sql.DB, log *slog.Logger, a *auth.Authenticator) *Handlers {
+	return &Handlers{db: db, log: log, auth: a}
+}
+
+// Register mounts the routes.
+func (h *Handlers) Register(mux *http.ServeMux) {
+	mux.HandleFunc("GET /api/v1/media-types", h.handleMediaTypes)
+
+	mux.Handle("GET /api/v1/libraries", h.auth.Require(h.handleList))
+	mux.Handle("GET /api/v1/libraries/{id}", h.auth.Require(h.handleGet))
+	mux.Handle("GET /api/v1/libraries/{id}/items", h.auth.Require(h.handleListItems))
+
+	mux.Handle("POST /api/v1/libraries", h.auth.RequireAdmin(http.HandlerFunc(h.handleCreate)))
+	mux.Handle("DELETE /api/v1/libraries/{id}", h.auth.RequireAdmin(http.HandlerFunc(h.handleDelete)))
+	mux.Handle("POST /api/v1/libraries/{id}/scan", h.auth.RequireAdmin(http.HandlerFunc(h.handleScan)))
+}
+
+// handleMediaTypes is public: the UI needs the list before login to render.
+func (h *Handlers) handleMediaTypes(w http.ResponseWriter, r *http.Request) {
+	httpx.WriteJSON(w, http.StatusOK, map[string]any{"media_types": SupportedTypes()})
+}
+
+func (h *Handlers) handleList(w http.ResponseWriter, r *http.Request, u auth.User) {
+	ids, err := auth.VisibleLibraryIDs(r.Context(), h.db, u)
+	if err != nil {
+		h.fail(w, "visible libraries", err)
+		return
+	}
+	libs, err := ListVisible(r.Context(), h.db, ids)
+	if err != nil {
+		h.fail(w, "list libraries", err)
+		return
+	}
+	httpx.WriteJSON(w, http.StatusOK, map[string]any{"libraries": libs})
+}
+
+func (h *Handlers) handleGet(w http.ResponseWriter, r *http.Request, u auth.User) {
+	id, ok := pathInt(w, r, "id")
+	if !ok {
+		return
+	}
+	allowed, err := auth.CanAccessLibrary(r.Context(), h.db, u, id)
+	if err != nil {
+		h.fail(w, "check access", err)
+		return
+	}
+	if !allowed {
+		// 404 rather than 403: an unauthorised user should not learn that a
+		// library exists.
+		httpx.WriteError(w, http.StatusNotFound, "library not found")
+		return
+	}
+	lib, err := Get(r.Context(), h.db, id)
+	if errors.Is(err, ErrNotFound) {
+		httpx.WriteError(w, http.StatusNotFound, "library not found")
+		return
+	}
+	if err != nil {
+		h.fail(w, "get library", err)
+		return
+	}
+	count, _ := CountItems(r.Context(), h.db, id)
+	httpx.WriteJSON(w, http.StatusOK, map[string]any{
+		"library":    lib,
+		"item_count": count,
+		"reachable":  RootExists(lib),
+	})
+}
+
+func (h *Handlers) handleCreate(w http.ResponseWriter, r *http.Request) {
+	var req struct {
+		Name     string `json:"name"`
+		Kind     string `json:"kind"`
+		RootPath string `json:"root_path"`
+	}
+	if err := httpx.DecodeJSON(r, &req); err != nil {
+		httpx.WriteError(w, http.StatusBadRequest, err.Error())
+		return
+	}
+
+	lib, err := Create(r.Context(), h.db, req.Name, req.Kind, req.RootPath)
+	switch {
+	case errors.Is(err, ErrNameExists):
+		httpx.WriteError(w, http.StatusConflict, "a library with that name already exists")
+		return
+	case errors.Is(err, ErrInvalidRoot), errors.Is(err, ErrUnknownKind):
+		httpx.WriteError(w, http.StatusBadRequest, err.Error())
+		return
+	case err != nil:
+		h.fail(w, "create library", err)
+		return
+	}
+
+	h.log.Info("library created", "name", lib.Name, "kind", lib.Kind, "path", lib.RootPath)
+	httpx.WriteJSON(w, http.StatusCreated, map[string]any{"library": lib})
+}
+
+func (h *Handlers) handleDelete(w http.ResponseWriter, r *http.Request) {
+	id, ok := pathInt(w, r, "id")
+	if !ok {
+		return
+	}
+	if err := Delete(r.Context(), h.db, id); errors.Is(err, ErrNotFound) {
+		httpx.WriteError(w, http.StatusNotFound, "library not found")
+		return
+	} else if err != nil {
+		h.fail(w, "delete library", err)
+		return
+	}
+	w.WriteHeader(http.StatusNoContent)
+}
+
+func (h *Handlers) handleScan(w http.ResponseWriter, r *http.Request) {
+	id, ok := pathInt(w, r, "id")
+	if !ok {
+		return
+	}
+	lib, err := Get(r.Context(), h.db, id)
+	if errors.Is(err, ErrNotFound) {
+		httpx.WriteError(w, http.StatusNotFound, "library not found")
+		return
+	}
+	if err != nil {
+		h.fail(w, "get library", err)
+		return
+	}
+
+	res, err := Scan(r.Context(), h.db, lib, h.log)
+	if err != nil {
+		h.fail(w, "scan library", err)
+		return
+	}
+	httpx.WriteJSON(w, http.StatusOK, res)
+}
+
+// handleListItems returns items in a library the caller may read.
+func (h *Handlers) handleListItems(w http.ResponseWriter, r *http.Request, u auth.User) {
+	id, ok := pathInt(w, r, "id")
+	if !ok {
+		return
+	}
+	allowed, err := auth.CanAccessLibrary(r.Context(), h.db, u, id)
+	if err != nil {
+		h.fail(w, "check access", err)
+		return
+	}
+	if !allowed {
+		httpx.WriteError(w, http.StatusNotFound, "library not found")
+		return
+	}
+
+	limit := 100
+	if v := r.URL.Query().Get("limit"); v != "" {
+		if n, err := strconv.Atoi(v); err == nil && n > 0 && n <= 500 {
+			limit = n
+		}
+	}
+
+	rows, err := h.db.QueryContext(r.Context(), `
+		SELECT id, kind, path, title, COALESCE(year, 0), added_at
+		FROM media_items
+		WHERE library_id = ? AND missing = 0
+		ORDER BY sort_title
+		LIMIT ?`, id, limit)
+	if err != nil {
+		h.fail(w, "list items", err)
+		return
+	}
+	defer rows.Close()
+
+	type itemDTO struct {
+		ID      int64  `json:"id"`
+		Kind    string `json:"kind"`
+		Path    string `json:"path"`
+		Title   string `json:"title"`
+		Year    int    `json:"year"`
+		AddedAt string `json:"added_at"`
+	}
+	items := []itemDTO{}
+	for rows.Next() {
+		var it itemDTO
+		if err := rows.Scan(&it.ID, &it.Kind, &it.Path, &it.Title, &it.Year, &it.AddedAt); err != nil {
+			h.fail(w, "scan items", err)
+			return
+		}
+		items = append(items, it)
+	}
+	if err := rows.Err(); err != nil {
+		h.fail(w, "iterate items", err)
+		return
+	}
+	httpx.WriteJSON(w, http.StatusOK, map[string]any{"items": items, "limit": limit})
+}
+
+// ── helpers ────────────────────────────────────────────────────────────
+
+func (h *Handlers) fail(w http.ResponseWriter, what string, err error) {
+	h.log.Error(what, "err", err)
+	httpx.WriteError(w, http.StatusInternalServerError, "internal server error")
+}
+
+func pathInt(w http.ResponseWriter, r *http.Request, name string) (int64, bool) {
+	n, err := strconv.ParseInt(r.PathValue(name), 10, 64)
+	if err != nil || n <= 0 {
+		httpx.WriteError(w, http.StatusBadRequest, "invalid "+name)
+		return 0, false
+	}
+	return n, true
+}
diff --git a/internal/library/library.go b/internal/library/library.go
new file mode 100644
index 0000000..298268c
--- /dev/null
+++ b/internal/library/library.go
@@ -0,0 +1,192 @@
+package library
+
+import (
+	"context"
+	"database/sql"
+	"errors"
+	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
+	"time"
+)
+
+var (
+	// ErrNotFound means no library matched.
+	ErrNotFound = errors.New("library: not found")
+	// ErrNameExists means the library name is taken.
+	ErrNameExists = errors.New("library: name already in use")
+	// ErrInvalidRoot means the root path is missing, not a directory, or not
+	// readable.
+	ErrInvalidRoot = errors.New("library: invalid root path")
+)
+
+// Library is a media root of a single kind.
+type Library struct {
+	ID        int64     `json:"id"`
+	Name      string    `json:"name"`
+	Kind      string    `json:"kind"`
+	RootPath  string    `json:"root_path"`
+	CreatedAt time.Time `json:"created_at"`
+}
+
+const librarySelect = `SELECT id, name, kind, root_path, created_at FROM libraries`
+
+// Create validates and inserts a library.
+//
+// The root path is resolved to an absolute, symlink-free path and must exist.
+// Storing the resolved form matters: the scanner compares filesystem paths
+// against this value, and "/media/../media" would silently match nothing.
+func Create(ctx context.Context, db *sql.DB, name, kind, rootPath string) (Library, error) {
+	name = strings.TrimSpace(name)
+	if name == "" {
+		return Library{}, errors.New("library: name must not be empty")
+	}
+	if err := ValidateKind(kind); err != nil {
+		return Library{}, err
+	}
+
+	resolved, err := resolveRoot(rootPath)
+	if err != nil {
+		return Library{}, err
+	}
+
+	var lib Library
+	var created string
+	err = db.QueryRowContext(ctx, `
+		INSERT INTO libraries (name, kind, root_path)
+		VALUES (?, ?, ?)
+		RETURNING id, created_at`,
+		name, strings.ToLower(kind), resolved,
+	).Scan(&lib.ID, &created)
+	if err != nil {
+		if isUnique(err) {
+			return Library{}, ErrNameExists
+		}
+		return Library{}, fmt.Errorf("library: create: %w", err)
+	}
+	lib.Name, lib.Kind, lib.RootPath = name, strings.ToLower(kind), resolved
+	lib.CreatedAt, _ = time.Parse(time.RFC3339Nano, created)
+	return lib, nil
+}
+
+// Get loads one library by id.
+func Get(ctx context.Context, db *sql.DB, id int64) (Library, error) {
+	return scanLibrary(db.QueryRowContext(ctx, librarySelect+` WHERE id = ?`, id))
+}
+
+// List returns all libraries.
+func List(ctx context.Context, db *sql.DB) ([]Library, error) {
+	return queryLibraries(ctx, db, librarySelect+` ORDER BY name`)
+}
+
+// ListVisible returns the libraries in the given id set. An empty set yields an
+// empty slice, never "all" — that distinction is the whole point of the
+// access-control model.
+func ListVisible(ctx context.Context, db *sql.DB, ids []int64) ([]Library, error) {
+	if len(ids) == 0 {
+		return []Library{}, nil
+	}
+	placeholders := make([]string, len(ids))
+	args := make([]any, len(ids))
+	for i, id := range ids {
+		placeholders[i] = "?"
+		args[i] = id
+	}
+	q := librarySelect + ` WHERE id IN (` + strings.Join(placeholders, ",") + `) ORDER BY name`
+	return queryLibraries(ctx, db, q, args...)
+}
+
+// Delete removes a library. Items, files, and grants cascade.
+func Delete(ctx context.Context, db *sql.DB, id int64) error {
+	res, err := db.ExecContext(ctx, `DELETE FROM libraries WHERE id = ?`, id)
+	if err != nil {
+		return fmt.Errorf("library: delete: %w", err)
+	}
+	n, _ := res.RowsAffected()
+	if n == 0 {
+		return ErrNotFound
+	}
+	return nil
+}
+
+// CountItems returns how many items a library holds (excluding missing).
+func CountItems(ctx context.Context, db *sql.DB, id int64) (int, error) {
+	var n int
+	err := db.QueryRowContext(ctx,
+		`SELECT count(*) FROM media_items WHERE library_id = ? AND missing = 0`, id).Scan(&n)
+	return n, err
+}
+
+// ── helpers ────────────────────────────────────────────────────────────
+
+func resolveRoot(rootPath string) (string, error) {
+	if strings.TrimSpace(rootPath) == "" {
+		return "", fmt.Errorf("%w: path is empty", ErrInvalidRoot)
+	}
+	abs, err := filepath.Abs(rootPath)
+	if err != nil {
+		return "", fmt.Errorf("%w: %v", ErrInvalidRoot, err)
+	}
+	if resolved, err := filepath.EvalSymlinks(abs); err == nil {
+		abs = resolved
+	} else {
+		return "", fmt.Errorf("%w: %v", ErrInvalidRoot, err)
+	}
+
+	info, err := os.Stat(abs)
+	if err != nil {
+		return "", fmt.Errorf("%w: %v", ErrInvalidRoot, err)
+	}
+	if !info.IsDir() {
+		return "", fmt.Errorf("%w: %s is not a directory", ErrInvalidRoot, abs)
+	}
+	// Confirm readability; a directory can exist and still deny access.
+	f, err := os.Open(abs)
+	if err != nil {
+		return "", fmt.Errorf("%w: %v", ErrInvalidRoot, err)
+	}
+	_ = f.Close()
+	return abs, nil
+}
+
+func queryLibraries(ctx context.Context, db *sql.DB, q string, args ...any) ([]Library, error) {
+	rows, err := db.QueryContext(ctx, q, args...)
+	if err != nil {
+		return nil, fmt.Errorf("library: query: %w", err)
+	}
+	defer rows.Close()
+
+	out := []Library{}
+	for rows.Next() {
+		lib, err := scanLibrary(rows)
+		if err != nil {
+			return nil, err
+		}
+		out = append(out, lib)
+	}
+	return out, rows.Err()
+}
+
+type scanner interface{ Scan(dest ...any) error }
+
+func scanLibrary(row scanner) (Library, error) {
+	var lib Library
+	var created string
+	if err := row.Scan(&lib.ID, &lib.Name, &lib.Kind, &lib.RootPath, &created); err != nil {
+		if errors.Is(err, sql.ErrNoRows) {
+			return Library{}, ErrNotFound
+		}
+		return Library{}, err
+	}
+	lib.CreatedAt, _ = time.Parse(time.RFC3339Nano, created)
+	return lib, nil
+}
+
+func isUnique(err error) bool {
+	if err == nil {
+		return false
+	}
+	msg := strings.ToUpper(err.Error())
+	return strings.Contains(msg, "UNIQUE CONSTRAINT FAILED") || strings.Contains(msg, "CONSTRAINT FAILED: UNIQUE")
+}
diff --git a/internal/library/library_test.go b/internal/library/library_test.go
new file mode 100644
index 0000000..2ab7f99
--- /dev/null
+++ b/internal/library/library_test.go
@@ -0,0 +1,111 @@
+package library
+
+import (
+	"context"
+	"database/sql"
+	"errors"
+	"io"
+	"log/slog"
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/mithral/vellum/internal/core"
+	"github.com/mithral/vellum/migrations"
+)
+
+func testDB(t *testing.T) *sql.DB {
+	t.Helper()
+	db, err := core.OpenDB(filepath.Join(t.TempDir(), "lib.db"))
+	if err != nil {
+		t.Fatalf("OpenDB: %v", err)
+	}
+	t.Cleanup(func() { _ = db.Close() })
+	log := slog.New(slog.NewTextHandler(io.Discard, nil))
+	if err := core.Migrate(context.Background(), db, migrations.FS, log); err != nil {
+		t.Fatalf("Migrate: %v", err)
+	}
+	return db
+}
+
+func testLogger() *slog.Logger {
+	return slog.New(slog.NewTextHandler(io.Discard, nil))
+}
+
+func writeFile(t *testing.T, path, content string) {
+	t.Helper()
+	if err := os.MkdirAll(filepath.Dir(path), 0o755); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(path, []byte(content), 0o644); err != nil {
+		t.Fatal(err)
+	}
+}
+
+func TestRegistryBasics(t *testing.T) {
+	if err := ValidateKind("ebooks"); err != nil {
+		t.Errorf("ebooks should be valid: %v", err)
+	}
+	if err := ValidateKind("nonsense"); !errors.Is(err, ErrUnknownKind) {
+		t.Errorf("nonsense kind error = %v, want ErrUnknownKind", err)
+	}
+	if k, ok := KindForExtension(".epub"); !ok || k != "ebooks" {
+		t.Errorf("KindForExtension(.epub) = %q,%v", k, ok)
+	}
+	if k, ok := KindForExtension("CBZ"); !ok || k != "comics" {
+		t.Errorf("KindForExtension(CBZ) = %q,%v (should be case-insensitive)", k, ok)
+	}
+	if len(SupportedTypes()) == 0 {
+		t.Error("no media types registered")
+	}
+}
+
+func TestCleanTitle(t *testing.T) {
+	cases := map[string]string{
+		"Project Hail Mary.epub":  "Project Hail Mary",
+		"the_hobbit.mobi":         "the hobbit",
+		"Book.Title.2020.epub":    "Book Title 2020",
+		"/deep/path/Saga 001.cbz": "Saga 001",
+	}
+	for in, want := range cases {
+		if got := CleanTitle(in); got != want {
+			t.Errorf("CleanTitle(%q) = %q, want %q", in, got, want)
+		}
+	}
+}
+
+func TestCreateLibraryValidation(t *testing.T) {
+	db := testDB(t)
+	ctx := context.Background()
+	root := t.TempDir()
+
+	if _, err := Create(ctx, db, "Good", "ebooks", root); err != nil {
+		t.Fatalf("valid create failed: %v", err)
+	}
+	if _, err := Create(ctx, db, "Good", "ebooks", root); !errors.Is(err, ErrNameExists) {
+		t.Errorf("duplicate name error = %v, want ErrNameExists", err)
+	}
+	if _, err := Create(ctx, db, "Bad", "nonsense", root); !errors.Is(err, ErrUnknownKind) {
+		t.Errorf("bad kind error = %v, want ErrUnknownKind", err)
+	}
+	if _, err := Create(ctx, db, "Bad", "ebooks", "/nope/not/here"); !errors.Is(err, ErrInvalidRoot) {
+		t.Errorf("bad root error = %v, want ErrInvalidRoot", err)
+	}
+}
+
+func TestListVisibleNeverMeansAll(t *testing.T) {
+	db := testDB(t)
+	ctx := context.Background()
+	root := t.TempDir()
+	if _, err := Create(ctx, db, "Ebooks", "ebooks", root); err != nil {
+		t.Fatal(err)
+	}
+
+	libs, err := ListVisible(ctx, db, nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(libs) != 0 {
+		t.Errorf("ListVisible(nil) returned %d libraries; empty set must mean none", len(libs))
+	}
+}
diff --git a/internal/library/registry.go b/internal/library/registry.go
new file mode 100644
index 0000000..114bc41
--- /dev/null
+++ b/internal/library/registry.go
@@ -0,0 +1,138 @@
+// Package library owns library definitions and the scanner that turns files on
+// disk into rows in media_items / media_files.
+//
+// Modules declare what file extensions they care about via RegisterType; this
+// package never imports a module.
+package library
+
+import (
+	"errors"
+	"fmt"
+	"path/filepath"
+	"sort"
+	"strings"
+	"sync"
+)
+
+// MediaType declares one kind of library and the file extensions it owns.
+type MediaType struct {
+	// Kind is the value stored in libraries.kind and media_items.kind.
+	Kind string
+	// Name is the human label shown in the UI.
+	Name string
+	// Extensions are lowercase, with a leading dot (".epub").
+	Extensions []string
+}
+
+// builtinTypes are the media types Vellum understands out of the box. Modules
+// may add more at runtime with RegisterType; these exist so the core is
+// useful before any module is wired up.
+var builtinTypes = []MediaType{
+	{Kind: "ebooks", Name: "Ebooks", Extensions: []string{".epub", ".mobi", ".azw3", ".fb2"}},
+	{Kind: "comics", Name: "Comics", Extensions: []string{".cbz", ".cbr", ".pdf"}},
+	{Kind: "audiobooks", Name: "Audiobooks", Extensions: []string{".m4b", ".mp3", ".m4a", ".opus", ".flac", ".ogg"}},
+	{Kind: "music", Name: "Music", Extensions: []string{".mp3", ".flac", ".m4a", ".opus", ".ogg", ".wav"}},
+	{Kind: "photos", Name: "Photos", Extensions: []string{".jpg", ".jpeg", ".png", ".webp", ".heic", ".gif", ".avif"}},
+	{Kind: "video", Name: "Video", Extensions: []string{".mkv", ".mp4", ".webm", ".avi", ".mov"}},
+}
+
+var (
+	typesMu   sync.RWMutex
+	types     = map[string]MediaType{}
+	extToKind = map[string]string{}
+)
+
+func init() {
+	for _, t := range builtinTypes {
+		registerTypeLocked(t)
+	}
+}
+
+// RegisterType adds or replaces a media type. Intended to be called from a
+// module's init or wiring function.
+func RegisterType(t MediaType) {
+	typesMu.Lock()
+	defer typesMu.Unlock()
+	registerTypeLocked(t)
+}
+
+func registerTypeLocked(t MediaType) {
+	t.Kind = strings.ToLower(strings.TrimSpace(t.Kind))
+	for i, e := range t.Extensions {
+		t.Extensions[i] = normalizeExt(e)
+	}
+	types[t.Kind] = t
+	for _, e := range t.Extensions {
+		// Last registration wins for a shared extension (e.g. .pdf is comics).
+		extToKind[e] = t.Kind
+	}
+}
+
+// SupportedTypes returns every registered media type, sorted by kind.
+func SupportedTypes() []MediaType {
+	typesMu.RLock()
+	defer typesMu.RUnlock()
+	out := make([]MediaType, 0, len(types))
+	for _, t := range types {
+		out = append(out, t)
+	}
+	sort.Slice(out, func(i, j int) bool { return out[i].Kind < out[j].Kind })
+	return out
+}
+
+// KindForExtension maps a file extension to the media kind that owns it.
+func KindForExtension(ext string) (string, bool) {
+	typesMu.RLock()
+	defer typesMu.RUnlock()
+	k, ok := extToKind[normalizeExt(ext)]
+	return k, ok
+}
+
+var (
+	// ErrUnknownKind means the requested media kind is not registered.
+	ErrUnknownKind = errors.New("library: unknown media kind")
+)
+
+// ValidateKind reports whether kind is a registered media type.
+func ValidateKind(kind string) error {
+	typesMu.RLock()
+	defer typesMu.RUnlock()
+	k := strings.ToLower(strings.TrimSpace(kind))
+	if _, ok := types[k]; !ok {
+		return fmt.Errorf("%w %q", ErrUnknownKind, kind)
+	}
+	return nil
+}
+
+// extensionsFor returns the extension set owned by a library kind.
+func extensionsFor(kind string) map[string]bool {
+	typesMu.RLock()
+	defer typesMu.RUnlock()
+	t, ok := types[kind]
+	if !ok {
+		return nil
+	}
+	set := make(map[string]bool, len(t.Extensions))
+	for _, e := range t.Extensions {
+		set[e] = true
+	}
+	return set
+}
+
+func normalizeExt(ext string) string {
+	ext = strings.ToLower(strings.TrimSpace(ext))
+	if ext != "" && !strings.HasPrefix(ext, ".") {
+		ext = "." + ext
+	}
+	return ext
+}
+
+// CleanTitle turns a filename into a human title: strips the extension,
+// collapses separators, and trims noise.
+func CleanTitle(filename string) string {
+	base := strings.TrimSuffix(filepath.Base(filename), filepath.Ext(filename))
+	base = strings.ReplaceAll(base, "_", " ")
+	base = strings.ReplaceAll(base, ".", " ")
+	base = strings.Join(strings.Fields(base), " ")
+	return strings.TrimSpace(base)
+}
diff --git a/internal/library/scan.go b/internal/library/scan.go
new file mode 100644
index 0000000..3542814
--- /dev/null
+++ b/internal/library/scan.go
@@ -0,0 +1,285 @@
+package library
+
+import (
+	"context"
+	"database/sql"
+	"fmt"
+	"io/fs"
+	"log/slog"
+	"os"
+	"path/filepath"
+	"strings"
+	"syscall"
+	"time"
+)
+
+// ScanResult summarises one scan pass.
+type ScanResult struct {
+	LibraryID int64    `json:"library_id"`
+	Scanned   int      `json:"scanned"`
+	Added     int      `json:"added"`
+	Updated   int      `json:"updated"`
+	Restored  int      `json:"restored"`
+	Missing   int      `json:"missing"`
+	Unchanged int      `json:"unchanged"`
+	Duration  int64    `json:"duration_ms"`
+	Errors    []string `json:"errors,omitempty"`
+}
+
+// candidate is a supported file found on disk.
+type candidate struct {
+	relPath string
+	size    int64
+	mtime   int64
+	inode   int64
+	ext     string
+}
+
+// knownFile is an existing row for this library.
+type knownFile struct {
+	itemID  int64
+	fileID  int64
+	size    int64
+	mtime   int64
+	missing bool
+}
+
+// Scan walks a library's root and reconciles it with the database.
+//
+// Files that changed are re-upserted; files that vanished are marked missing
+// rather than deleted, so their progress survives a temporarily unavailable
+// mount. A scan never fails because of a single unreadable file — it records
+// the error and continues, because a partial library is better than none.
+func Scan(ctx context.Context, db *sql.DB, lib Library, log *slog.Logger) (ScanResult, error) {
+	start := time.Now()
+	res := ScanResult{LibraryID: lib.ID}
+
+	exts := extensionsFor(lib.Kind)
+	if len(exts) == 0 {
+		return res, fmt.Errorf("library %d: no extensions registered for kind %q", lib.ID, lib.Kind)
+	}
+
+	// 1. What do we already know?
+	known, err := loadKnownFiles(ctx, db, lib.ID)
+	if err != nil {
+		return res, err
+	}
+
+	// 2. What is on disk?
+	found, errs := walkRoot(lib.RootPath, exts)
+	res.Errors = errs
+
+	// 3. Reconcile in one transaction.
+	tx, err := db.BeginTx(ctx, nil)
+	if err != nil {
+		return res, err
+	}
+	defer tx.Rollback() //nolint:errcheck
+
+	now := time.Now().UTC().Format(time.RFC3339Nano)
+	for rel, c := range found {
+		res.Scanned++
+		prev, exists := known[rel]
+
+		switch {
+		case exists && !prev.missing && prev.size == c.size && prev.mtime == c.mtime:
+			res.Unchanged++
+			continue
+
+		case exists && prev.missing:
+			res.Restored++
+		case exists:
+			res.Updated++
+		default:
+			res.Added++
+		}
+
+		itemID, err := upsertItem(ctx, tx, lib, rel, c)
+		if err != nil {
+			res.Errors = append(res.Errors, fmt.Sprintf("%s: %v", rel, err))
+			continue
+		}
+		if err := upsertFile(ctx, tx, itemID, rel, c); err != nil {
+			res.Errors = append(res.Errors, fmt.Sprintf("%s: %v", rel, err))
+			continue
+		}
+	}
+
+	// 4. Anything we knew about that is gone.
+	for rel := range known {
+		if _, ok := found[rel]; ok {
+			continue
+		}
+		if err := markMissing(ctx, tx, lib.ID, rel, now); err != nil {
+			res.Errors = append(res.Errors, fmt.Sprintf("%s: %v", rel, err))
+			continue
+		}
+		res.Missing++
+	}
+
+	if err := tx.Commit(); err != nil {
+		return res, fmt.Errorf("library: commit scan: %w", err)
+	}
+
+	res.Duration = time.Since(start).Milliseconds()
+	log.Info("scan complete",
+		"library", lib.Name, "kind", lib.Kind,
+		"scanned", res.Scanned, "added", res.Added, "updated", res.Updated,
+		"restored", res.Restored, "missing", res.Missing, "unchanged", res.Unchanged,
+		"duration_ms", res.Duration, "errors", len(res.Errors))
+	return res, nil
+}
+
+// walkRoot collects supported files under root, keyed by slash-separated
+// path relative to root.
+func walkRoot(root string, exts map[string]bool) (map[string]candidate, []string) {
+	out := make(map[string]candidate)
+	var errs []string
+
+	err := filepath.WalkDir(root, func(path string, d fs.DirEntry, err error) error {
+		if err != nil {
+			errs = append(errs, fmt.Sprintf("%s: %v", path, err))
+			// An unreadable directory should not abort the walk.
+			if d != nil && d.IsDir() {
+				return fs.SkipDir
+			}
+			return nil
+		}
+
+		name := d.Name()
+		if d.IsDir() {
+			if path != root && strings.HasPrefix(name, ".") {
+				return fs.SkipDir
+			}
+			return nil
+		}
+		if strings.HasPrefix(name, ".") {
+			return nil
+		}
+
+		ext := strings.ToLower(filepath.Ext(name))
+		if !exts[ext] {
+			return nil
+		}
+
+		info, err := d.Info()
+		if err != nil {
+			errs = append(errs, fmt.Sprintf("%s: %v", path, err))
+			return nil
+		}
+		if !info.Mode().IsRegular() {
+			return nil
+		}
+
+		rel, err := filepath.Rel(root, path)
+		if err != nil {
+			errs = append(errs, fmt.Sprintf("%s: %v", path, err))
+			return nil
+		}
+
+		c := candidate{
+			relPath: filepath.ToSlash(rel),
+			size:    info.Size(),
+			mtime:   info.ModTime().UnixNano(),
+			ext:     strings.TrimPrefix(ext, "."),
+		}
+		if st, ok := info.Sys().(*syscall.Stat_t); ok {
+			c.inode = int64(st.Ino)
+		}
+		out[c.relPath] = c
+		return nil
+	})
+	if err != nil {
+		errs = append(errs, fmt.Sprintf("%s: %v", root, err))
+	}
+	return out, errs
+}
+
+func loadKnownFiles(ctx context.Context, db *sql.DB, libraryID int64) (map[string]knownFile, error) {
+	rows, err := db.QueryContext(ctx, `
+		SELECT f.path, f.item_id, f.id, f.size, f.mtime, f.missing
+		FROM media_files f
+		JOIN media_items i ON i.id = f.item_id
+		WHERE i.library_id = ?`, libraryID)
+	if err != nil {
+		return nil, fmt.Errorf("library: load known files: %w", err)
+	}
+	defer rows.Close()
+
+	out := make(map[string]knownFile)
+	for rows.Next() {
+		var (
+			absPath string
+			kf      knownFile
+			mtime   string
+			missing int
+		)
+		if err := rows.Scan(&absPath, &kf.itemID, &kf.fileID, &kf.size, &mtime, &missing); err != nil {
+			return nil, err
+		}
+		kf.mtime = parseUnixNano(mtime)
+		kf.missing = missing == 1
+		out[absPath] = kf
+	}
+	return out, rows.Err()
+}
+
+func upsertItem(ctx context.Context, tx *sql.Tx, lib Library, rel string, c candidate) (int64, error) {
+	title := CleanTitle(rel)
+	var id int64
+	err := tx.QueryRowContext(ctx, `
+		INSERT INTO media_items (library_id, kind, path, title, sort_title, missing)
+		VALUES (?, ?, ?, ?, ?, 0)
+		ON CONFLICT (library_id, path)
+		DO UPDATE SET missing = 0
+		RETURNING id`,
+		lib.ID, lib.Kind, rel, title, strings.ToLower(title),
+	).Scan(&id)
+	if err != nil {
+		return 0, fmt.Errorf("upsert item: %w", err)
+	}
+	return id, nil
+}
+
+func upsertFile(ctx context.Context, tx *sql.Tx, itemID int64, rel string, c candidate) error {
+	_, err := tx.ExecContext(ctx, `
+		INSERT INTO media_files (item_id, path, size, mtime, inode, container, missing)
+		VALUES (?, ?, ?, ?, ?, ?, 0)
+		ON CONFLICT (path)
+		DO UPDATE SET item_id = excluded.item_id, size = excluded.size,
+		              mtime = excluded.mtime, inode = excluded.inode,
+		              container = excluded.container, missing = 0`,
+		itemID, rel, c.size, fmt.Sprint(c.mtime), c.inode, c.ext)
+	if err != nil {
+		return fmt.Errorf("upsert file: %w", err)
+	}
+	return nil
+}
+
+func markMissing(ctx context.Context, tx *sql.Tx, libraryID int64, rel, now string) error {
+	if _, err := tx.ExecContext(ctx,
+		`UPDATE media_files SET missing = 1 WHERE path = ?`, rel); err != nil {
+		return err
+	}
+	_, err := tx.ExecContext(ctx, `
+		UPDATE media_items SET missing = 1
+		WHERE library_id = ? AND path = ?`, libraryID, rel)
+	return err
+}
+
+func parseUnixNano(s string) int64 {
+	var n int64
+	for i := 0; i < len(s); i++ {
+		if s[i] < '0' || s[i] > '9' {
+			return 0
+		}
+		n = n*10 + int64(s[i]-'0')
+	}
+	return n
+}
+
+// RootExists reports whether a library's root is currently reachable.
+func RootExists(lib Library) bool {
+	info, err := os.Stat(lib.RootPath)
+	return err == nil && info.IsDir()
+}
diff --git a/internal/library/scan_test.go b/internal/library/scan_test.go
new file mode 100644
index 0000000..ffa7a05
--- /dev/null
+++ b/internal/library/scan_test.go
@@ -0,0 +1,130 @@
+package library
+
+import (
+	"context"
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestScanLifecycle(t *testing.T) {
+	db := testDB(t)
+	ctx := context.Background()
+	root := t.TempDir()
+
+	writeFile(t, filepath.Join(root, "a.epub"), "aaaaaaaaaa")
+	writeFile(t, filepath.Join(root, "b.epub"), "bbbbbbbbbbbbbbbbbbbb")
+	writeFile(t, filepath.Join(root, "sub", "c.epub"), "cccccccccccccccccccccccccccccc")
+	writeFile(t, filepath.Join(root, "notes.txt"), "not media")
+	writeFile(t, filepath.Join(root, ".hidden.epub"), "hidden")
+	writeFile(t, filepath.Join(root, ".git", "d.epub"), "in a hidden dir")
+
+	lib, err := Create(ctx, db, "Ebooks", "ebooks", root)
+	if err != nil {
+		t.Fatalf("Create: %v", err)
+	}
+
+	// First scan: three supported files, nothing else.
+	res, err := Scan(ctx, db, lib, testLogger())
+	if err != nil {
+		t.Fatalf("Scan: %v", err)
+	}
+	if res.Added != 3 || res.Scanned != 3 {
+		t.Fatalf("first scan added=%d scanned=%d, want 3/3 (%+v)", res.Added, res.Scanned, res)
+	}
+	if n, _ := CountItems(ctx, db, lib.ID); n != 3 {
+		t.Errorf("item count = %d, want 3", n)
+	}
+
+	// Second scan: nothing changed.
+	res, err = Scan(ctx, db, lib, testLogger())
+	if err != nil {
+		t.Fatal(err)
+	}
+	if res.Unchanged != 3 || res.Added != 0 || res.Updated != 0 {
+		t.Errorf("second scan unchanged=%d added=%d updated=%d, want 3/0/0", res.Unchanged, res.Added, res.Updated)
+	}
+
+	// Modify a.epub (different size).
+	writeFile(t, filepath.Join(root, "a.epub"), "aaaaaaaaaaaaaaaaaaaaaaaaaaaa")
+	res, err = Scan(ctx, db, lib, testLogger())
+	if err != nil {
+		t.Fatal(err)
+	}
+	if res.Updated != 1 || res.Unchanged != 2 {
+		t.Errorf("after modify updated=%d unchanged=%d, want 1/2", res.Updated, res.Unchanged)
+	}
+
+	// Delete b.epub: it goes missing, it is not deleted.
+	if err := os.Remove(filepath.Join(root, "b.epub")); err != nil {
+		t.Fatal(err)
+	}
+	res, err = Scan(ctx, db, lib, testLogger())
+	if err != nil {
+		t.Fatal(err)
+	}
+	if res.Missing != 1 {
+		t.Errorf("after delete missing=%d, want 1", res.Missing)
+	}
+	if n, _ := CountItems(ctx, db, lib.ID); n != 2 {
+		t.Errorf("item count (excluding missing) = %d, want 2", n)
+	}
+
+	// The row still exists, flagged missing.
+	var missing int
+	if err := db.QueryRowContext(ctx,
+		`SELECT missing FROM media_items WHERE library_id = ? AND path = ?`, lib.ID, "b.epub").Scan(&missing); err != nil {
+		t.Fatalf("missing item row was deleted: %v", err)
+	}
+	if missing != 1 {
+		t.Errorf("missing flag = %d, want 1", missing)
+	}
+
+	// Restore b.epub.
+	writeFile(t, filepath.Join(root, "b.epub"), "bbbbbbbbbbbbbbbbbbbb")
+	res, err = Scan(ctx, db, lib, testLogger())
+	if err != nil {
+		t.Fatal(err)
+	}
+	if res.Restored != 1 {
+		t.Errorf("after restore restored=%d, want 1 (%+v)", res.Restored, res)
+	}
+	if n, _ := CountItems(ctx, db, lib.ID); n != 3 {
+		t.Errorf("item count after restore = %d, want 3", n)
+	}
+}
+
+func TestScanUnreadableRoot(t *testing.T) {
+	db := testDB(t)
+	ctx := context.Background()
+	root := t.TempDir()
+	writeFile(t, filepath.Join(root, "a.epub"), "x")
+
+	lib, err := Create(ctx, db, "Ebooks", "ebooks", root)
+	if err != nil {
+		t.Fatal(err)
+	}
+	// Index it once so there is a known file to go missing.
+	if _, err := Scan(ctx, db, lib, testLogger()); err != nil {
+		t.Fatal(err)
+	}
+
+	// Remove the root out from under the library.
+	if err := os.RemoveAll(root); err != nil {
+		t.Fatal(err)
+	}
+
+	res, err := Scan(ctx, db, lib, testLogger())
+	if err != nil {
+		t.Fatalf("scan should not fail on a missing root: %v", err)
+	}
+	if res.Added != 0 {
+		t.Errorf("added=%d, want 0", res.Added)
+	}
+	if res.Missing != 1 {
+		t.Errorf("missing=%d, want 1 (existing item now vanished)", res.Missing)
+	}
+	if len(res.Errors) == 0 {
+		t.Error("expected the walk error to be recorded")
+	}
+}
diff --git a/migrations/0002_missing.sql b/migrations/0002_missing.sql
new file mode 100644
index 0000000..8fd77d9
--- /dev/null
+++ b/migrations/0002_missing.sql
@@ -0,0 +1,13 @@
+-- 0002_missing.sql — track files that disappear from disk.
+--
+-- A rescan must not delete an item whose file is temporarily unavailable
+-- (unmounted drive, NFS hiccup, user mid-reorganise). Deleting cascades into
+-- progress, which is the one thing in this schema that cannot be regenerated.
+-- Mark instead, and filter on read. A later pass can prune rows that have been
+-- missing for a long time.
+
+ALTER TABLE media_items ADD COLUMN missing INTEGER NOT NULL DEFAULT 0;
+ALTER TABLE media_files ADD COLUMN missing INTEGER NOT NULL DEFAULT 0;
+
+CREATE INDEX idx_items_library_missing ON media_items(library_id, missing);
+CREATE INDEX idx_files_missing ON media_files(missing);