diff --git a/README.md b/README.md
index 8928c53..8e4f3ab 100644
--- a/README.md
+++ b/README.md
@@ -116,6 +116,13 @@ ensure this connection is preserved.
 
 Without these rules, your Kobo will eventually lose its connection to `readeckobo`.
 
+## 📚 Optional: Syncing Books
+
+`readeckobo` can optionally double as a reverse proxy for a self-hosted book service such as
+[Grimmory](https://github.com/grimmory-tools/grimmory) or [Komga](https://komga.org), so a single
+Kobo device can sync both articles and books. This is opt-in and off by default — see the
+"Book Sync" section of [docs/CONFIG.md](docs/CONFIG.md) for configuration.
+
 ## 🔒 A Quick Word on Security
 
 A little security goes a long way.
diff --git a/config.yaml.example b/config.yaml.example
index c5fc544..62c7169 100644
--- a/config.yaml.example
+++ b/config.yaml.example
@@ -6,3 +6,6 @@ readeck:
 users:
   - token: "a-very-secret-token-for-your-kobo"
     readeck_access_token: "your-plain-text-readeck-access-token"
+    # Only used if book_sync is enabled below. See docs/CONFIG.md.
+    # book_service_url: "https://grimmory.example.com/api/kobo/grimmory-token"
+book_sync: false
diff --git a/docs/CONFIG.md b/docs/CONFIG.md
index a12e47b..49e0a8b 100644
--- a/docs/CONFIG.md
+++ b/docs/CONFIG.md
@@ -10,6 +10,7 @@ This document provides a detailed reference for all available configuration opti
 | `log_level` | Output verbosity. Options: `debug`, `info`, `warn`, `error`. | String | `info` | No |
 | `readeck.host` | The full base URL of your Readeck instance. | URL String | - | **Yes** |
 | `users` | A list of Kobo-to-Readeck user mappings. | List of Objects | - | **Yes** |
+| `book_sync` | Proxy book sync to a self-hosted book service. See [Book Sync](#book-sync-optional) below. | Boolean | `false` | No |
 
 ## User Object
 
@@ -19,6 +20,7 @@ Each entry in the `users` list maps a Kobo device identity to a Readeck account.
 | :--- | :--- |
 | `token` | A unique UUID used to identify the Kobo device. This is the **Plain Text** token generated by the `bin/generate-encrypted-token.sh` script. |
 | `readeck_access_token` | The API token for the Readeck account you want to sync. |
+| `book_service_url` | Optional. This user's book service endpoint, used when `book_sync` is enabled. |
 
 ### How to get a Readeck API Token
 
@@ -41,3 +43,25 @@ users:
   - token: "550e8400-e29b-41d4-a716-446655440000" # From generate-encrypted-token.sh
     readeck_access_token: "rdk_..."              # From Readeck Profile
 ```
+
+## Book Sync (optional)
+
+readeckobo can optionally proxy book sync to a self-hosted book service such as
+[Grimmory](https://github.com/grimmory-tools/grimmory) or [Komga](https://komga.org), so a Kobo can
+sync both articles (via readeckobo) and books through one of these services. Enable `book_sync`,
+and set each user's `book_service_url` to the Kobo endpoint provided by that service:
+
+```yaml
+book_sync: true
+
+users:
+  - token: "550e8400-e29b-41d4-a716-446655440000"
+    readeck_access_token: "rdk_..."
+    book_service_url: "https://grimmory.example.com/api/kobo/grimmory-token"
+```
+
+Point the Kobo's `api_endpoint` at `https://readeckobo.example.com/booksync/<USER_TOKEN>` - that's the
+user's readeckobo `token` - and update your nginx config, see `nginx.conf.snippet`.
+
+Your proxy must set `X-Forwarded-Host` and `X-Forwarded-Proto`. The service must be configured to
+forward to the Kobo Store (in Grimmory, **Forward to Kobo Store**).
\ No newline at end of file
diff --git a/internal/app/app.go b/internal/app/app.go
index 988b494..7a712cf 100644
--- a/internal/app/app.go
+++ b/internal/app/app.go
@@ -714,6 +714,78 @@ func (a *App) newReadeckClient(readeckToken string) (*readeck.Client, error) {
 	return readeck.NewClient(a.Config.Readeck.Host, readeckToken, a.Logger, a.ReadeckHTTPClient)
 }
 
+func (a *App) HandleBookSync(w http.ResponseWriter, r *http.Request) {
+	deviceToken := r.PathValue("deviceToken")
+
+	upstream, ok := a.Config.ResolveBookSyncUpstream(deviceToken)
+	if !ok {
+		http.NotFound(w, r)
+		return
+	}
+
+	target, err := url.Parse(upstream)
+	if err != nil {
+		a.Logger.Errorf("Error parsing book_sync endpoint %q: %v", upstream, err)
+		return
+	}
+
+	rest := strings.TrimPrefix(r.URL.Path, "/booksync/"+deviceToken)
+	isInit := strings.HasSuffix(rest, "/v1/initialization")
+
+	proxy := httputil.NewSingleHostReverseProxy(target)
+	originalDirector := proxy.Director
+	proxy.Director = func(req *http.Request) {
+		req.URL.Path, req.URL.RawPath = rest, ""
+		originalDirector(req)
+		req.Host = target.Host
+		if isInit {
+			// So ModifyResponse below sees plaintext to rewrite.
+			req.Header.Set("Accept-Encoding", "identity")
+		}
+	}
+
+	if isInit {
+		base := a.instapaperBase(r)
+		proxy.ModifyResponse = func(resp *http.Response) error {
+			body, err := io.ReadAll(resp.Body)
+			if err != nil {
+				return err
+			}
+			if err := resp.Body.Close(); err != nil {
+				return err
+			}
+
+			body = bytes.ReplaceAll(body, []byte("https://www.instapaper.com"), []byte(base))
+
+			resp.Body = io.NopCloser(bytes.NewReader(body))
+			resp.ContentLength = int64(len(body))
+			resp.Header.Set("Content-Length", strconv.Itoa(len(body)))
+			resp.Header.Del("Content-Encoding")
+			return nil
+		}
+	}
+
+	proxy.ServeHTTP(w, r)
+}
+
+func (a *App) instapaperBase(r *http.Request) string {
+	scheme := r.Header.Get("X-Forwarded-Proto")
+	if scheme == "" {
+		if r.TLS == nil {
+			scheme = "http"
+		} else {
+			scheme = "https"
+		}
+	}
+
+	host := r.Header.Get("X-Forwarded-Host")
+	if host == "" {
+		host = r.Host
+	}
+
+	return scheme + "://" + host + "/instapaper-proxy/instapaper"
+}
+
 func (a *App) HandleDumpAndForward(w http.ResponseWriter, r *http.Request) {
 	a.Logger.Debugf("Dumping request from %s", r.RemoteAddr)
 	a.Logger.Debugf("Method: %s", r.Method)
diff --git a/internal/app/app_test.go b/internal/app/app_test.go
index 4465e34..b1f4f46 100644
--- a/internal/app/app_test.go
+++ b/internal/app/app_test.go
@@ -8,6 +8,7 @@ import (
 	"net/http"
 	"net/http/httptest"
 	"net/url" // Added this import
+	"strconv"
 	"strings"
 	"testing"
 
@@ -843,4 +844,95 @@ func TestHandleConvertImage(t *testing.T) {
 	})
 }
 
+func TestHandleBookSync(t *testing.T) {
+	t.Run("unknown token returns 404", func(t *testing.T) {
+		app := NewApp(
+			WithConfig(&config.Config{
+				BookSync: true,
+				Users: []config.User{
+					{Token: "device-token", ReadeckAccessToken: "rt", BookServiceURL: "https://grimmory.example.com/api/kobo/g1"},
+				},
+			}),
+			WithLogger(testLogger),
+		)
+
+		req := httptest.NewRequest(http.MethodGet, "/booksync/unknown-token/v1/library/sync", nil)
+		req.SetPathValue("deviceToken", "unknown-token")
+		rr := httptest.NewRecorder()
+
+		app.HandleBookSync(rr, req)
+
+		if rr.Code != http.StatusNotFound {
+			t.Errorf("expected status %d, got %d", http.StatusNotFound, rr.Code)
+		}
+	})
+
+	t.Run("non-initialization requests are proxied byte-for-byte", func(t *testing.T) {
+		upstream := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			if r.URL.Path != "/api/kobo/grimmory-token/v1/library/sync" {
+				t.Errorf("unexpected upstream path: %s", r.URL.Path)
+			}
+			w.Header().Set("Content-Type", "application/json")
+			_, _ = w.Write([]byte(`{"entries": []}`))
+		}))
+		defer upstream.Close()
+
+		app := NewApp(
+			WithConfig(&config.Config{
+				BookSync: true,
+				Users: []config.User{
+					{Token: "device-token", ReadeckAccessToken: "rt", BookServiceURL: upstream.URL + "/api/kobo/grimmory-token"},
+				},
+			}),
+			WithLogger(testLogger),
+		)
+
+		req := httptest.NewRequest(http.MethodGet, "/booksync/device-token/v1/library/sync", nil)
+		req.SetPathValue("deviceToken", "device-token")
+		rr := httptest.NewRecorder()
+
+		app.HandleBookSync(rr, req)
+
+		if rr.Code != http.StatusOK {
+			t.Errorf("expected status %d, got %d", http.StatusOK, rr.Code)
+		}
+		if got := rr.Body.String(); got != `{"entries": []}` {
+			t.Errorf("expected passthrough body, got %q", got)
+		}
+	})
+
+	t.Run("initialization response has instapaper.com rewritten", func(t *testing.T) {
+		goldenBody := `{"instapaper":"https://www.instapaper.com"}`
+		upstream := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			_, _ = w.Write([]byte(goldenBody))
+		}))
+		defer upstream.Close()
+
+		app := NewApp(
+			WithConfig(&config.Config{
+				BookSync: true,
+				Users: []config.User{
+					{Token: "device-token", ReadeckAccessToken: "rt", BookServiceURL: upstream.URL + "/api/kobo/grimmory-token"},
+				},
+			}),
+			WithLogger(testLogger),
+		)
+
+		req := httptest.NewRequest(http.MethodGet, "/booksync/device-token/v1/initialization", nil)
+		req.Host = "readeckobo.example.com"
+		req.SetPathValue("deviceToken", "device-token")
+		rr := httptest.NewRecorder()
+
+		app.HandleBookSync(rr, req)
+
+		want := `{"instapaper":"http://readeckobo.example.com/instapaper-proxy/instapaper"}`
+		if got := rr.Body.String(); got != want {
+			t.Errorf("body = %q, want %q", got, want)
+		}
+		if got := rr.Header().Get("Content-Length"); got != strconv.Itoa(len(want)) {
+			t.Errorf("Content-Length = %q, want %q", got, strconv.Itoa(len(want)))
+		}
+	})
+}
+
 
diff --git a/internal/config/config.go b/internal/config/config.go
index 5c3e6a7..7d9f540 100644
--- a/internal/config/config.go
+++ b/internal/config/config.go
@@ -14,6 +14,7 @@ import (
 type User struct {
 	Token              string `koanf:"token" validate:"required"`
 	ReadeckAccessToken string `koanf:"readeck_access_token" validate:"required"`
+	BookServiceURL     string `koanf:"book_service_url" validate:"omitempty,url"`
 }
 
 type ConfigReadeck struct {
@@ -27,12 +28,16 @@ type Config struct {
 	} `koanf:"server"`
 	Users    []User        `koanf:"users" validate:"required,min=1,dive"`
 	LogLevel string        `koanf:"log_level" validate:"oneof=error warn info debug"`
+	BookSync bool          `koanf:"book_sync"`
 }
 
 func (c *Config) Validate() error {
 	validate := validator.New()
 	err := validate.Struct(c)
 	if err == nil {
+		if c.BookSync && !c.hasBookServiceURL() {
+			return fmt.Errorf("configuration validation failed: book_sync is enabled but no user has book_service_url set")
+		}
 		return nil
 	}
 
@@ -44,6 +49,30 @@ func (c *Config) Validate() error {
 	return err
 }
 
+func (c *Config) hasBookServiceURL() bool {
+	for _, u := range c.Users {
+		if u.BookServiceURL != "" {
+			return true
+		}
+	}
+
+	return false
+}
+
+func (c *Config) ResolveBookSyncUpstream(deviceToken string) (string, bool) {
+	if !c.BookSync {
+		return "", false
+	}
+
+	for _, u := range c.Users {
+		if u.Token == deviceToken && u.BookServiceURL != "" {
+			return u.BookServiceURL, true
+		}
+	}
+
+	return "", false
+}
+
 func Load(path string) (*Config, error) {
 	k := koanf.New(".")
 	parser := yaml.Parser()
diff --git a/internal/config/config_test.go b/internal/config/config_test.go
index e1a2499..51a4cc0 100644
--- a/internal/config/config_test.go
+++ b/internal/config/config_test.go
@@ -121,6 +121,39 @@ func TestLoad(t *testing.T) {
 			yamlContent: "readeck: \"should be a map but is a string\"",
 			wantErr:     true,
 		},
+		{
+			name: "valid config with book_sync",
+			config: map[string]any{
+				"readeck": map[string]any{
+					"host": "https://readeck.example.com",
+				},
+				"book_sync": true,
+				"users": []map[string]any{
+					{
+						"token":                "test-token",
+						"readeck_access_token": "test-readeck-token",
+						"book_service_url":     "https://grimmory.example.com/api/kobo/grimmory-token",
+					},
+				},
+			},
+			wantErr: false,
+		},
+		{
+			name: "invalid config book_sync enabled without any book_service_url",
+			config: map[string]any{
+				"readeck": map[string]any{
+					"host": "https://readeck.example.com",
+				},
+				"book_sync": true,
+				"users": []map[string]any{
+					{
+						"token":                "test-token",
+						"readeck_access_token": "test-readeck-token",
+					},
+				},
+			},
+			wantErr: true,
+		},
 	}
 
 	for _, tt := range tests {
@@ -162,3 +195,61 @@ func TestLoad(t *testing.T) {
 		})
 	}
 }
+
+func TestResolveBookSyncUpstream(t *testing.T) {
+	tests := []struct {
+		name         string
+		cfg          Config
+		deviceToken  string
+		wantUpstream string
+		wantOK       bool
+	}{
+		{
+			name: "disabled returns false even with a configured url",
+			cfg: Config{
+				BookSync: false,
+				Users: []User{
+					{Token: "t1", BookServiceURL: "https://grimmory.example.com/api/kobo/g1"},
+				},
+			},
+			deviceToken: "t1",
+			wantOK:      false,
+		},
+		{
+			name: "matching device token returns that user's endpoint",
+			cfg: Config{
+				BookSync: true,
+				Users: []User{
+					{Token: "t1", BookServiceURL: "https://grimmory.example.com/api/kobo/g1"},
+					{Token: "t2", BookServiceURL: "https://grimmory.example.com/api/kobo/g2"},
+				},
+			},
+			deviceToken:  "t2",
+			wantUpstream: "https://grimmory.example.com/api/kobo/g2",
+			wantOK:       true,
+		},
+		{
+			name: "unknown device token returns false",
+			cfg: Config{
+				BookSync: true,
+				Users: []User{
+					{Token: "t1", BookServiceURL: "https://grimmory.example.com/api/kobo/g1"},
+				},
+			},
+			deviceToken: "unknown-token",
+			wantOK:      false,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			gotUpstream, gotOK := tt.cfg.ResolveBookSyncUpstream(tt.deviceToken)
+			if gotOK != tt.wantOK {
+				t.Errorf("ResolveBookSyncUpstream() ok = %v, want %v", gotOK, tt.wantOK)
+			}
+			if gotUpstream != tt.wantUpstream {
+				t.Errorf("ResolveBookSyncUpstream() upstream = %q, want %q", gotUpstream, tt.wantUpstream)
+			}
+		})
+	}
+}
diff --git a/internal/webserver/webserver.go b/internal/webserver/webserver.go
index 97a8b42..f81d6ca 100644
--- a/internal/webserver/webserver.go
+++ b/internal/webserver/webserver.go
@@ -22,6 +22,10 @@ func ListenAndServe(port int, application *app.App, logger *logger.Logger) {
 	mux.HandleFunc("/api/convert-image", application.HandleConvertImage)
 	mux.HandleFunc("/instapaper-proxy/storeapi/v1/initialization", application.HandleDumpAndForward)
 
+	if application.Config.BookSync {
+		mux.HandleFunc("/booksync/{deviceToken}/", application.HandleBookSync)
+	}
+
 	// Catch-all for unimplemented routes
 	mux.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
 		logger.Warnf("404 Not Found: URL=%s, Method=%s, Params=%v", r.URL.Path, r.Method, r.URL.Query())
diff --git a/nginx.conf.snippet b/nginx.conf.snippet
index 3cbbd39..341b892 100644
--- a/nginx.conf.snippet
+++ b/nginx.conf.snippet
@@ -28,3 +28,14 @@
                 proxy_set_header X-Forwarded-Proto $scheme;
                 proxy_set_header X-Forwarded-Prefix /instapaper-proxy/instapaper;
         }
+
+        # Optional: if you enable `book_sync` in config.yaml, use this instead of the
+        # /instapaper-proxy/storeapi* blocks above (see docs/CONFIG.md).
+        # location /booksync/ {
+        #         proxy_pass http://readeckobo-upstream;
+        #         proxy_set_header Host $host;
+        #         proxy_set_header X-Forwarded-Proto $scheme;
+        #         proxy_set_header X-Forwarded-Host $host;
+        #         client_max_body_size 128M;
+        #         proxy_buffer_size 128k;
+        # }