diff --git a/crates/wzp-proto/src/packet.rs b/crates/wzp-proto/src/packet.rs
index c35c2ff..47447f4 100644
--- a/crates/wzp-proto/src/packet.rs
+++ b/crates/wzp-proto/src/packet.rs
@@ -670,6 +670,10 @@ pub struct RoomParticipant {
     pub fingerprint: String,
     /// Optional display name set by the client.
     pub alias: Option<String>,
+    /// Relay label — identifies which relay this participant is connected to.
+    /// None for local participants, Some("Relay B") for federated.
+    #[serde(default)]
+    pub relay_label: Option<String>,
 }
 
 /// Reasons for ending a call.
diff --git a/desktop/src-tauri/src/engine.rs b/desktop/src-tauri/src/engine.rs
index e06aabc..692159d 100644
--- a/desktop/src-tauri/src/engine.rs
+++ b/desktop/src-tauri/src/engine.rs
@@ -45,6 +45,7 @@ unsafe impl Sync for SyncWrapper {}
 pub struct ParticipantInfo {
     pub fingerprint: String,
     pub alias: Option<String>,
+    pub relay_label: Option<String>,
 }
 
 pub struct EngineStatus {
@@ -346,6 +347,7 @@ impl CallEngine {
                             .map(|p| ParticipantInfo {
                                 fingerprint: p.fingerprint,
                                 alias: p.alias,
+                                relay_label: p.relay_label,
                             })
                             .collect();
                         let count = unique.len();
@@ -395,6 +397,7 @@ impl CallEngine {
                 .map(|p| ParticipantInfo {
                     fingerprint: p.fingerprint.clone(),
                     alias: p.alias.clone(),
+                    relay_label: p.relay_label.clone(),
                 })
                 .collect()
         }; // lock dropped here
diff --git a/desktop/src-tauri/src/main.rs b/desktop/src-tauri/src/main.rs
index 9958a09..1ce3568 100644
--- a/desktop/src-tauri/src/main.rs
+++ b/desktop/src-tauri/src/main.rs
@@ -18,6 +18,7 @@ struct CallEvent {
 struct Participant {
     fingerprint: String,
     alias: Option<String>,
+    relay_label: Option<String>,
 }
 
 #[derive(Clone, Serialize)]
@@ -195,6 +196,7 @@ async fn get_status(state: tauri::State<'_, Arc<AppState>>) -> Result<CallStatus
                 .map(|p| Participant {
                     fingerprint: p.fingerprint,
                     alias: p.alias,
+                    relay_label: p.relay_label,
                 })
                 .collect(),
             encode_fps: status.frames_sent,
diff --git a/desktop/src/main.ts b/desktop/src/main.ts
index 014b95f..5267f6a 100644
--- a/desktop/src/main.ts
+++ b/desktop/src/main.ts
@@ -540,32 +540,49 @@ async function pollStatus() {
     const pct = rms > 0 ? Math.min(100, (Math.log(rms) / Math.log(32767)) * 100) : 0;
     levelBar.style.width = `${pct}%`;
 
-    // Participants with identicons
+    // Participants grouped by relay
     if (st.participants.length === 0) {
       participantsDiv.innerHTML = '<div class="participants-empty">Waiting for participants...</div>';
     } else {
       participantsDiv.innerHTML = "";
-      st.participants.forEach((p) => {
-        const name = p.alias || "Anonymous";
-        const fp = p.fingerprint || "";
-        const isMe = fp && myFingerprint.includes(fp);
+      // Group by relay_label (null = this relay)
+      const groups: Record<string, typeof st.participants> = {};
+      st.participants.forEach((p: any) => {
+        const relay = p.relay_label || "This Relay";
+        if (!groups[relay]) groups[relay] = [];
+        groups[relay].push(p);
+      });
 
-        const row = document.createElement("div");
-        row.className = "participant";
+      Object.entries(groups).forEach(([relay, members]) => {
+        // Relay header
+        const header = document.createElement("div");
+        header.className = "relay-group-header";
+        const isLocal = relay === "This Relay";
+        header.innerHTML = `<span class="relay-dot-small ${isLocal ? "green" : "blue"}"></span> ${escapeHtml(relay)}`;
+        participantsDiv.appendChild(header);
 
-        // Identicon avatar
-        const icon = createIdenticonEl(fp || name, 36, true);
-        if (isMe) icon.style.outline = "2px solid var(--accent)";
-        row.appendChild(icon);
+        // Participants under this relay
+        (members as any[]).forEach((p) => {
+          const name = p.alias || "Anonymous";
+          const fp = p.fingerprint || "";
+          const isMe = fp && myFingerprint.includes(fp);
 
-        const info = document.createElement("div");
-        info.className = "info";
-        info.innerHTML = `
-          <div class="name">${escapeHtml(name)} ${isMe ? '<span class="you-badge">you</span>' : ""}</div>
-          <div class="fp">${escapeHtml(fp ? fp.substring(0, 16) : "")}</div>
-        `;
-        row.appendChild(info);
-        participantsDiv.appendChild(row);
+          const row = document.createElement("div");
+          row.className = "participant";
+
+          const icon = createIdenticonEl(fp || name, 36, true);
+          if (isMe) icon.style.outline = "2px solid var(--accent)";
+          row.appendChild(icon);
+
+          const info = document.createElement("div");
+          info.className = "info";
+          info.innerHTML = `
+            <div class="name">${escapeHtml(name)} ${isMe ? '<span class="you-badge">you</span>' : ""}</div>
+            <div class="fp">${escapeHtml(fp ? fp.substring(0, 16) : "")}</div>
+          `;
+          row.appendChild(info);
+          participantsDiv.appendChild(row);
+        });
       });
     }
 
diff --git a/desktop/src/style.css b/desktop/src/style.css
index 5d03216..33984be 100644
--- a/desktop/src/style.css
+++ b/desktop/src/style.css
@@ -441,6 +441,35 @@ button.primary:disabled { opacity: 0.5; cursor: not-allowed; }
   border-radius: 8px;
 }
 
+/* ── Relay group headers ── */
+.relay-group-header {
+  display: flex;
+  align-items: center;
+  gap: 6px;
+  font-size: 11px;
+  text-transform: uppercase;
+  letter-spacing: 0.5px;
+  color: var(--text-dim);
+  padding: 6px 0 2px;
+  border-top: 1px solid #ffffff08;
+  margin-top: 4px;
+}
+
+.relay-group-header:first-child {
+  border-top: none;
+  margin-top: 0;
+}
+
+.relay-dot-small {
+  width: 6px;
+  height: 6px;
+  border-radius: 50%;
+  display: inline-block;
+}
+
+.relay-dot-small.green { background: var(--green); }
+.relay-dot-small.blue { background: #60a5fa; }
+
 /* ── Controls ── */
 .controls {
   display: flex;