diff --git a/src/db/repository/device.rs b/src/db/repository/device.rs
index 18a8516..2d02c1c 100644
--- a/src/db/repository/device.rs
+++ b/src/db/repository/device.rs
@@ -1,3 +1,4 @@
+use chrono::{DateTime, Utc};
 use diesel::prelude::*;
 
 use super::SqliteRepository;
@@ -95,4 +96,35 @@ impl gpodder::DeviceRepository for SqliteRepository {
 
         Ok(())
     }
+
+    fn merge_sync_groups(
+        &self,
+        user: &gpodder::User,
+        device_ids: Vec<&str>,
+    ) -> Result<i64, gpodder::AuthErr> {
+        todo!()
+    }
+
+    fn remove_from_sync_group(
+        &self,
+        user: &gpodder::User,
+        device_ids: Vec<&str>,
+    ) -> Result<(), gpodder::AuthErr> {
+        todo!()
+    }
+
+    fn synchronize_sync_group(
+        &self,
+        group_id: i64,
+        time_changed: DateTime<Utc>,
+    ) -> Result<(), gpodder::AuthErr> {
+        todo!()
+    }
+
+    fn devices_by_sync_group(
+        &self,
+        user: &gpodder::User,
+    ) -> Result<(Vec<gpodder::Device>, Vec<Vec<gpodder::Device>>), gpodder::AuthErr> {
+        todo!()
+    }
 }
diff --git a/src/gpodder/mod.rs b/src/gpodder/mod.rs
index fe904d4..7d26b84 100644
--- a/src/gpodder/mod.rs
+++ b/src/gpodder/mod.rs
@@ -63,13 +63,44 @@ pub trait DeviceRepository {
     fn devices_for_user(&self, user: &User) -> Result<Vec<Device>, AuthErr>;
 
     /// Update the information for the given device. If the device doesn't exist yet, it should be
-    /// created.
+    /// created without a sync group.
     fn update_device_info(
         &self,
         user: &User,
         device_id: &str,
         patch: DevicePatch,
     ) -> Result<(), AuthErr>;
+
+    /// Add the devices to the same sync group by:
+    ///
+    /// * Merging the sync groups of all devices already in a sync group
+    /// * Adding all devices not yet in a sync group to the newly merged sync group
+    ///
+    /// # Returns
+    ///
+    /// ID of the final sync group
+    fn merge_sync_groups(&self, user: &User, device_ids: Vec<&str>) -> Result<i64, AuthErr>;
+
+    /// Synchronize the sync group by adding or removing subscriptions to each device so that each
+    /// device's subscription state is the same
+    fn synchronize_sync_group(
+        &self,
+        group_id: i64,
+        time_changed: DateTime<Utc>,
+    ) -> Result<(), AuthErr>;
+
+    /// Remove the devices from their respective sync groups
+    fn remove_from_sync_group(&self, user: &User, device_ids: Vec<&str>) -> Result<(), AuthErr>;
+
+    /// Return all devices for the user, grouped per sync group
+    ///
+    /// # Returns
+    ///
+    /// A tuple (unsynced devices, sync groups)
+    fn devices_by_sync_group(
+        &self,
+        user: &User,
+    ) -> Result<(Vec<Device>, Vec<Vec<Device>>), AuthErr>;
 }
 
 pub trait SubscriptionRepository {
@@ -83,7 +114,8 @@ pub trait SubscriptionRepository {
     /// Return all subscriptions for a given user
     fn subscriptions_for_user(&self, user: &User) -> Result<Vec<models::Subscription>, AuthErr>;
 
-    /// Replace the list of subscriptions for a device with the given list
+    /// Replace the list of subscriptions for a device and all devices in its sync group with the
+    /// given list
     fn set_subscriptions_for_device(
         &self,
         user: &User,
@@ -92,7 +124,8 @@ pub trait SubscriptionRepository {
         time_changed: DateTime<Utc>,
     ) -> Result<(), AuthErr>;
 
-    /// Update the list of subscriptions for a device by adding and removing the given URLs
+    /// Update the list of subscriptions for a device and all devices in its sync group by adding
+    /// and removing the given URLs
     fn update_subscriptions_for_device(
         &self,
         user: &User,
diff --git a/src/gpodder/repository.rs b/src/gpodder/repository.rs
index e55d010..4cc17be 100644
--- a/src/gpodder/repository.rs
+++ b/src/gpodder/repository.rs
@@ -94,6 +94,22 @@ impl GpodderRepository {
         self.store.update_device_info(user, device_id, patch)
     }
 
+    pub fn update_device_sync_status(
+        &self,
+        user: &models::User,
+        sync: Vec<Vec<&str>>,
+        unsync: Vec<&str>,
+    ) -> Result<(), AuthErr> {
+        todo!("perform diff devices to sync and unsync")
+    }
+
+    pub fn devices_by_sync_group(
+        &self,
+        user: &models::User,
+    ) -> Result<(Vec<models::Device>, Vec<Vec<models::Device>>), AuthErr> {
+        self.store.devices_by_sync_group(user)
+    }
+
     pub fn subscriptions_for_device(
         &self,
         user: &models::User,