diff --git a/README.md b/README.md
index 5e16c3a..6ccdb36 100644
--- a/README.md
+++ b/README.md
@@ -78,6 +78,16 @@ Watch a folder for new CBZ/CBR files and optimize them automatically:
 cbzconverter watch [folder] --quality 85 --override --format webp --split
 ```
 
+Watch mode only reacts to filesystem events that occur *after* it starts; by default it does
+not scan and optimize files that already exist in the folder when it starts. Run the
+`optimize` command first if you need to process an existing library, then use `watch`
+to keep it up to date going forward, or pass `--backfill` to have `watch` optimize the
+existing files at startup before it begins watching for new changes. The only exception
+is a directory that gets created/moved into the watched tree while watch mode is
+running: since no per-file event is emitted for files already inside it, its existing
+archives are always processed once when the directory is first detected, regardless of
+`--backfill`.
+
 Or with Docker:
 
 ```sh
@@ -94,6 +104,7 @@ docker run -v /path/to/comics:/comics ghcr.io/belphemur/cbzoptimizer:latest watc
   - Can be specified as: `--format webp`, `-f webp`, or `--format=webp`
   - Case-insensitive: `webp`, `WEBP`, and `WebP` are all valid
 - `--timeout`, `-t`: Maximum time allowed for converting a single chapter (e.g., 30s, 5m, 1h). 0 means no timeout. Default is 0.
+- `--backfill`: *(`watch` only)* Optimize CBZ/CBR files that already exist in the watched folder at startup, before watching for new changes. Default is false.
 - `--log`, `-l`: Set log level; can be 'panic', 'fatal', 'error', 'warn', 'info', 'debug', or 'trace'. Default is info.
 
 ## Logging
diff --git a/cmd/cbzoptimizer/commands/watch_command.go b/cmd/cbzoptimizer/commands/watch_command.go
index b3bcb3e..3e82d8e 100644
--- a/cmd/cbzoptimizer/commands/watch_command.go
+++ b/cmd/cbzoptimizer/commands/watch_command.go
@@ -41,6 +41,9 @@ func init() {
 	// Setup common flags (format, quality, override, split, timeout) with viper binding
 	setupCommonFlags(command, &converterType, 85, true, false, true)
 
+	command.Flags().Bool("backfill", false, "Optimize CBZ/CBR files that already exist in the watched folder at startup, before watching for new changes")
+	_ = viper.BindPFlag("backfill", command.Flags().Lookup("backfill"))
+
 	AddCommand(command)
 }
 func WatchCommand(_ *cobra.Command, args []string) error {
@@ -64,6 +67,8 @@ func WatchCommand(_ *cobra.Command, args []string) error {
 
 	timeout := viper.GetDuration("timeout")
 
+	backfill := viper.GetBool("backfill")
+
 	converterType := constant.FindConversionFormat(viper.GetString("format"))
 	chapterConverter, err := converter.Get(converterType)
 	if err != nil {
@@ -74,7 +79,7 @@ func WatchCommand(_ *cobra.Command, args []string) error {
 	if err != nil {
 		return fmt.Errorf("failed to prepare converter: %w", err)
 	}
-	log.Info().Str("path", path).Bool("override", override).Uint8("quality", quality).Str("format", converterType.String()).Bool("split", split).Msg("Watching directory")
+	log.Info().Str("path", path).Bool("override", override).Uint8("quality", quality).Str("format", converterType.String()).Bool("split", split).Bool("backfill", backfill).Msg("Watching directory")
 
 	watcher, err := fsnotify.NewWatcher()
 	if err != nil {
@@ -100,10 +105,17 @@ func WatchCommand(_ *cobra.Command, args []string) error {
 	debouncer := newEventDebouncer(debounceDelay, queue.Enqueue)
 	defer debouncer.Stop()
 
+	// Note: existing archives already present under path when the watch
+	// starts are left untouched unless --backfill is set. Watch mode only
+	// reacts to filesystem events going forward by default; use the
+	// `optimize` command (or pass --backfill) to process a library's
+	// existing contents. Archives inside a directory that is created/moved
+	// into the watched tree *after* startup are always back-filled below,
+	// since only the directory itself generates an fsnotify event.
 	if err := addRecursiveWatch(watcher, path); err != nil {
 		return fmt.Errorf("failed to watch path %s: %w", path, err)
 	}
-	backfillExistingArchives(path, debouncer.Trigger)
+	maybeBackfillExistingArchives(backfill, path, debouncer.Trigger)
 
 	for {
 		select {
@@ -194,6 +206,17 @@ func backfillExistingArchives(rootPath string, process func(path string)) {
 	}
 }
 
+// maybeBackfillExistingArchives runs backfillExistingArchives against
+// rootPath only when enabled is true. It exists as its own function (rather
+// than inlining the `if` check at the call site) so the gating decision used
+// by WatchCommand can be exercised directly in tests.
+func maybeBackfillExistingArchives(enabled bool, rootPath string, process func(path string)) {
+	if !enabled {
+		return
+	}
+	backfillExistingArchives(rootPath, process)
+}
+
 func shouldProcessWatchEvent(event fsnotify.Event) bool {
 	return event.Has(fsnotify.Create) || event.Has(fsnotify.Write) || event.Has(fsnotify.Rename)
 }
diff --git a/cmd/cbzoptimizer/commands/watch_command_test.go b/cmd/cbzoptimizer/commands/watch_command_test.go
index 485c3fd..0484511 100644
--- a/cmd/cbzoptimizer/commands/watch_command_test.go
+++ b/cmd/cbzoptimizer/commands/watch_command_test.go
@@ -170,3 +170,35 @@ func TestOptimizeQueueSkipsMissingPath(t *testing.T) {
 
 	assert.EqualValues(t, 1, atomic.LoadInt32(&calls))
 }
+
+func TestWatchCommandBackfillFlagDefaultsToFalse(t *testing.T) {
+	watchCmd, _, err := rootCmd.Find([]string{"watch"})
+	require.NoError(t, err)
+
+	flag := watchCmd.Flags().Lookup("backfill")
+	require.NotNil(t, flag, "watch command should register a --backfill flag")
+	assert.Equal(t, "false", flag.DefValue)
+	assert.Equal(t, "bool", flag.Value.Type())
+}
+
+func TestMaybeBackfillExistingArchivesOnlyInvokedWhenRequested(t *testing.T) {
+	root := t.TempDir()
+	require.NoError(t, os.WriteFile(filepath.Join(root, "chapter1.cbz"), []byte("data"), 0o644))
+
+	runBackfill := func(enabled bool) []string {
+		var found []string
+		var mu sync.Mutex
+		process := func(path string) {
+			mu.Lock()
+			defer mu.Unlock()
+			found = append(found, path)
+		}
+		// This is the exact same gating call WatchCommand makes based on the
+		// --backfill flag value.
+		maybeBackfillExistingArchives(enabled, root, process)
+		return found
+	}
+
+	assert.Empty(t, runBackfill(false), "no pre-existing archive should be processed when backfill is disabled")
+	assert.Len(t, runBackfill(true), 1, "pre-existing archives should be processed when backfill is enabled")
+}
diff --git a/docs/project-overview.md b/docs/project-overview.md
index 0a566c2..1531dfe 100644
--- a/docs/project-overview.md
+++ b/docs/project-overview.md
@@ -19,7 +19,7 @@ CBZOptimizer is a Go CLI that optimizes comic archives (`.cbz` and `.cbr`) by co
 
 ## Watch mode
 
-`watch` monitors a directory tree for archive file changes and runs optimization automatically.
+`watch` monitors a directory tree for archive file changes and runs optimization automatically. By default it only reacts to changes going forward; pass `--backfill` to also optimize archives that already exist in the folder at startup.
 
 ## Key runtime requirements