diff --git a/CHANGELOG.md b/CHANGELOG.md
index 30be73c..7591dc6 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,7 @@
 - Sheets: add `sheets insert` to insert rows/columns into a sheet. (#203) — thanks @andybergon.
 - Sheets: add `sheets links` (alias `hyperlinks`) to list cell links from ranges, including rich-text links. (#374) — thanks @omothm.
 - Sheets: add `sheets create --parent` to place new spreadsheets in a Drive folder. (#424) — thanks @ManManavadaria.
+- Calendar: add `calendar subscribe` (aliases `sub`, `add-calendar`) to add a shared calendar to the current account’s calendar list. (#327) — thanks @cdthompson.
 - Gmail: add `watch serve --history-types` filtering (`messageAdded|messageDeleted|labelAdded|labelRemoved`) and include `deletedMessageIds` in webhook payloads. (#168) — thanks @salmonumbrella.
 - Contacts: support `--org`, `--title`, `--url`, `--note`, and `--custom` on create/update; include custom fields in get output with deterministic ordering. (#199) — thanks @phuctm97.
 - Drive: add `drive ls --all` (alias `--global`) to list across all accessible files; make `--all` and `--parent` mutually exclusive. (#107) — thanks @struong.
diff --git a/internal/cmd/calendar.go b/internal/cmd/calendar.go
index d15e810..e20c7b7 100644
--- a/internal/cmd/calendar.go
+++ b/internal/cmd/calendar.go
@@ -125,6 +125,10 @@ func (c *CalendarSubscribeCmd) Run(ctx context.Context, flags *RootFlags) error
 	if calendarID == "" {
 		return usage("calendarId required")
 	}
+	colorID, err := validateCalendarColorId(c.ColorID)
+	if err != nil {
+		return err
+	}
 
 	svc, err := newCalendarService(ctx, account)
 	if err != nil {
@@ -136,8 +140,8 @@ func (c *CalendarSubscribeCmd) Run(ctx context.Context, flags *RootFlags) error
 		Hidden:   c.Hidden,
 		Selected: c.Selected,
 	}
-	if c.ColorID != "" {
-		entry.ColorId = c.ColorID
+	if colorID != "" {
+		entry.ColorId = colorID
 	}
 
 	added, err := svc.CalendarList.Insert(entry).Do()
diff --git a/internal/cmd/calendar_validate.go b/internal/cmd/calendar_validate.go
index 6fa9811..b7cd456 100644
--- a/internal/cmd/calendar_validate.go
+++ b/internal/cmd/calendar_validate.go
@@ -27,6 +27,21 @@ func validateColorId(s string) (string, error) {
 	return s, nil
 }
 
+func validateCalendarColorId(s string) (string, error) {
+	s = strings.TrimSpace(s)
+	if s == "" {
+		return "", nil
+	}
+	id, err := strconv.Atoi(s)
+	if err != nil {
+		return "", fmt.Errorf("invalid calendar color ID: %q (must be 1-24)", s)
+	}
+	if id < 1 || id > 24 {
+		return "", fmt.Errorf("calendar color ID must be 1-24 (got %d)", id)
+	}
+	return s, nil
+}
+
 func validateVisibility(s string) (string, error) {
 	s = strings.TrimSpace(strings.ToLower(s))
 	if s == "" {
diff --git a/internal/cmd/calendar_validate_test.go b/internal/cmd/calendar_validate_test.go
index e3faa7f..1e510ac 100644
--- a/internal/cmd/calendar_validate_test.go
+++ b/internal/cmd/calendar_validate_test.go
@@ -17,6 +17,21 @@ func TestValidateColorID(t *testing.T) {
 	}
 }
 
+func TestValidateCalendarColorID(t *testing.T) {
+	if got, err := validateCalendarColorId(""); err != nil || got != "" {
+		t.Fatalf("expected empty ok, got %q %v", got, err)
+	}
+	if got, err := validateCalendarColorId("24"); err != nil || got != "24" {
+		t.Fatalf("expected valid id, got %q %v", got, err)
+	}
+	if _, err := validateCalendarColorId("25"); err == nil {
+		t.Fatalf("expected error for out of range")
+	}
+	if _, err := validateCalendarColorId("nope"); err == nil {
+		t.Fatalf("expected error for non-numeric")
+	}
+}
+
 func TestValidateVisibilityMore(t *testing.T) {
 	if got, err := validateVisibility(""); err != nil || got != "" {
 		t.Fatalf("expected empty ok, got %q %v", got, err)
diff --git a/internal/cmd/execute_calendar_test.go b/internal/cmd/execute_calendar_test.go
index ac7f24f..59e7806 100644
--- a/internal/cmd/execute_calendar_test.go
+++ b/internal/cmd/execute_calendar_test.go
@@ -124,6 +124,63 @@ func TestExecute_CalendarSubscribe_JSON(t *testing.T) {
 	}
 }
 
+func TestExecute_CalendarSubscribe_Flags(t *testing.T) {
+	origNew := newCalendarService
+	t.Cleanup(func() { newCalendarService = origNew })
+
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if !(strings.Contains(r.URL.Path, "calendarList") && r.Method == http.MethodPost) {
+			http.NotFound(w, r)
+			return
+		}
+
+		var req struct {
+			ID       string `json:"id"`
+			ColorID  string `json:"colorId"`
+			Hidden   bool   `json:"hidden"`
+			Selected bool   `json:"selected"`
+		}
+		if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
+			http.Error(w, err.Error(), http.StatusBadRequest)
+			return
+		}
+		if req.ID != "team@example.com" {
+			t.Fatalf("unexpected calendar id: %q", req.ID)
+		}
+		if req.ColorID != "24" {
+			t.Fatalf("unexpected color id: %q", req.ColorID)
+		}
+		if !req.Hidden {
+			t.Fatalf("expected hidden=true")
+		}
+		if req.Selected {
+			t.Fatalf("expected selected=false")
+		}
+
+		w.Header().Set("Content-Type", "application/json")
+		_ = json.NewEncoder(w).Encode(map[string]any{
+			"id":         req.ID,
+			"summary":    "Team Calendar",
+			"accessRole": "reader",
+		})
+	}))
+	defer srv.Close()
+
+	svc, err := calendar.NewService(context.Background(),
+		option.WithoutAuthentication(),
+		option.WithHTTPClient(srv.Client()),
+		option.WithEndpoint(srv.URL+"/"),
+	)
+	if err != nil {
+		t.Fatalf("NewService: %v", err)
+	}
+	newCalendarService = func(context.Context, string) (*calendar.Service, error) { return svc, nil }
+
+	if err := Execute([]string{"--account", "a@b.com", "calendar", "subscribe", "--color-id", "24", "--hidden", "--no-selected", "team@example.com"}); err != nil {
+		t.Fatalf("Execute: %v", err)
+	}
+}
+
 func TestExecute_CalendarSubscribe_Text(t *testing.T) {
 	origNew := newCalendarService
 	t.Cleanup(func() { newCalendarService = origNew })