diff --git a/crates/lavina-core/migrations/3_dialogs.sql b/crates/lavina-core/migrations/3_dialogs.sql
new file mode 100644
index 0000000..799628e
--- /dev/null
+++ b/crates/lavina-core/migrations/3_dialogs.sql
@@ -0,0 +1,14 @@
+create table dialogs(
+    participant_1 integer not null,
+    participant_2 integer not null,
+    created_at timestamp not null,
+    message_count integer not null default 0,
+    primary key (participant_1, participant_2)
+);
+
+create table dialog_messages(
+    dialog_id integer not null,
+    id integer not null,  -- unique per dialog, sequential in one dialog
+    content string not null,
+    primary key (dialog_id, id)
+);
diff --git a/crates/lavina-core/src/dialog.rs b/crates/lavina-core/src/dialog.rs
new file mode 100644
index 0000000..35157ea
--- /dev/null
+++ b/crates/lavina-core/src/dialog.rs
@@ -0,0 +1,75 @@
+//! Domain of dialogs – conversations between two participants.
+//!
+//! Dialogs are different from rooms in that they are always between two participants.
+//! There are no
+
+use std::collections::HashMap;
+use std::sync::Arc;
+
+use tokio::sync::RwLock as AsyncRwLock;
+
+use crate::player::PlayerId;
+use crate::repo::Storage;
+
+/// Id of a conversation between two players.
+///
+/// Dialogs are identified by the pair of participants' ids. The order of ids does not matter.
+#[derive(Debug, Clone, PartialEq, Eq, Hash)]
+pub struct DialogId(PlayerId, PlayerId);
+impl DialogId {
+    pub fn new(a: PlayerId, b: PlayerId) -> DialogId {
+        if a.as_inner() < b.as_inner() {
+            DialogId(a, b)
+        } else {
+            DialogId(b, a)
+        }
+    }
+
+    pub fn as_inner(&self) -> (&PlayerId, &PlayerId) {
+        (&self.0, &self.1)
+    }
+
+    pub fn into_inner(self) -> (PlayerId, PlayerId) {
+        (self.0, self.1)
+    }
+}
+
+struct Dialog {
+    storage_id: u32,
+    id: DialogId,
+    message_count: u32,
+}
+
+struct DialogRegistryInner {
+    dialogs: HashMap<DialogId, AsyncRwLock<Dialog>>,
+    storage: Storage,
+}
+
+#[derive(Clone)]
+pub struct DialogRegistry(Arc<AsyncRwLock<DialogRegistryInner>>);
+
+impl DialogRegistry {
+    pub fn new(storage: Storage) -> DialogRegistry {
+        DialogRegistry(Arc::new(AsyncRwLock::new(DialogRegistryInner {
+            dialogs: HashMap::new(),
+            storage,
+        })))
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_dialog_id_new() {
+        let a = PlayerId::from("a").unwrap();
+        let b = PlayerId::from("b").unwrap();
+        let id1 = DialogId::new(a.clone(), b.clone());
+        let id2 = DialogId::new(a.clone(), b.clone());
+        // Dialog ids are invariant with respect to the order of participants
+        assert_eq!(id1, id2);
+        assert_eq!(id1.as_inner(), (&a, &b));
+        assert_eq!(id2.as_inner(), (&a, &b));
+    }
+}
diff --git a/crates/lavina-core/src/lib.rs b/crates/lavina-core/src/lib.rs
index ff52363..1e5b861 100644
--- a/crates/lavina-core/src/lib.rs
+++ b/crates/lavina-core/src/lib.rs
@@ -2,10 +2,12 @@
 use anyhow::Result;
 use prometheus::Registry as MetricsRegistry;
 
+use crate::dialog::DialogRegistry;
 use crate::player::PlayerRegistry;
 use crate::repo::Storage;
 use crate::room::RoomRegistry;
 
+pub mod dialog;
 pub mod player;
 pub mod prelude;
 pub mod repo;
@@ -18,6 +20,7 @@ mod table;
 pub struct LavinaCore {
     pub players: PlayerRegistry,
     pub rooms: RoomRegistry,
+    pub dialogs: DialogRegistry,
 }
 
 impl LavinaCore {
@@ -25,7 +28,12 @@ impl LavinaCore {
         // TODO shutdown all services in reverse order on error
         let rooms = RoomRegistry::new(&mut metrics, storage.clone())?;
         let players = PlayerRegistry::empty(rooms.clone(), storage.clone(), &mut metrics)?;
-        Ok(LavinaCore { players, rooms })
+        let dialogs = DialogRegistry::new(storage.clone());
+        Ok(LavinaCore {
+            players,
+            rooms,
+            dialogs,
+        })
     }
 
     pub async fn shutdown(mut self) -> Result<()> {