diff --git a/frontend/src/components/common/HostKeyDialog.vue b/frontend/src/components/common/HostKeyDialog.vue
new file mode 100644
index 0000000..862d7b8
--- /dev/null
+++ b/frontend/src/components/common/HostKeyDialog.vue
@@ -0,0 +1,105 @@
+<template>
+  <Teleport to="body">
+    <div class="fixed inset-0 z-50 flex items-center justify-center">
+      <!-- Backdrop -->
+      <div
+        class="absolute inset-0 bg-black/60"
+        @click="emit('reject')"
+      />
+
+      <!-- Dialog -->
+      <div class="relative bg-[var(--wraith-bg-secondary)] border border-[var(--wraith-border)] rounded-lg shadow-2xl w-[480px] max-w-[90vw]">
+        <!-- Header -->
+        <div
+          class="flex items-center gap-3 px-5 py-4 border-b border-[var(--wraith-border)]"
+          :class="isChanged ? 'bg-red-500/10' : ''"
+        >
+          <!-- Warning icon for changed keys -->
+          <svg
+            v-if="isChanged"
+            class="w-6 h-6 text-[var(--wraith-accent-red)] shrink-0"
+            viewBox="0 0 16 16"
+            fill="currentColor"
+          >
+            <path d="M6.457 1.047c.659-1.234 2.427-1.234 3.086 0l6.082 11.378A1.75 1.75 0 0 1 14.082 15H1.918a1.75 1.75 0 0 1-1.543-2.575L6.457 1.047zM8 5a.75.75 0 0 0-.75.75v2.5a.75.75 0 0 0 1.5 0v-2.5A.75.75 0 0 0 8 5zm1 6a1 1 0 1 0-2 0 1 1 0 0 0 2 0z" />
+          </svg>
+          <!-- Lock icon for new keys -->
+          <svg
+            v-else
+            class="w-6 h-6 text-[var(--wraith-accent-blue)] shrink-0"
+            viewBox="0 0 16 16"
+            fill="currentColor"
+          >
+            <path d="M4 4a4 4 0 0 1 8 0v2h.25c.966 0 1.75.784 1.75 1.75v5.5A1.75 1.75 0 0 1 12.25 15h-8.5A1.75 1.75 0 0 1 2 13.25v-5.5C2 6.784 2.784 6 3.75 6H4V4zm8.25 3.5h-8.5a.25.25 0 0 0-.25.25v5.5c0 .138.112.25.25.25h8.5a.25.25 0 0 0 .25-.25v-5.5a.25.25 0 0 0-.25-.25zM10.5 4a2.5 2.5 0 1 0-5 0v2h5V4z" />
+          </svg>
+
+          <div>
+            <h2 class="text-sm font-semibold text-[var(--wraith-text-primary)]">
+              {{ isChanged ? 'HOST KEY HAS CHANGED' : 'Unknown Host Key' }}
+            </h2>
+            <p class="text-xs text-[var(--wraith-text-muted)] mt-0.5">
+              {{ isChanged ? 'The server key does not match the stored key!' : 'This host has not been seen before.' }}
+            </p>
+          </div>
+        </div>
+
+        <!-- Body -->
+        <div class="px-5 py-4 space-y-3">
+          <p v-if="isChanged" class="text-xs text-[var(--wraith-accent-red)]">
+            WARNING: This could indicate a man-in-the-middle attack. Only accept if you know the host key was recently changed.
+          </p>
+
+          <div class="space-y-2">
+            <div class="flex items-center gap-2 text-xs">
+              <span class="text-[var(--wraith-text-muted)] w-16 shrink-0">Host:</span>
+              <span class="text-[var(--wraith-text-primary)] font-mono">{{ hostname }}</span>
+            </div>
+            <div class="flex items-center gap-2 text-xs">
+              <span class="text-[var(--wraith-text-muted)] w-16 shrink-0">Key type:</span>
+              <span class="text-[var(--wraith-text-primary)] font-mono">{{ keyType }}</span>
+            </div>
+            <div class="flex items-start gap-2 text-xs">
+              <span class="text-[var(--wraith-text-muted)] w-16 shrink-0">Fingerprint:</span>
+              <span class="text-[var(--wraith-accent-blue)] font-mono break-all select-text">{{ fingerprint }}</span>
+            </div>
+          </div>
+        </div>
+
+        <!-- Footer -->
+        <div class="flex items-center justify-end gap-3 px-5 py-3 border-t border-[var(--wraith-border)]">
+          <button
+            class="px-4 py-1.5 text-xs rounded bg-[var(--wraith-bg-tertiary)] text-[var(--wraith-text-secondary)] hover:text-[var(--wraith-text-primary)] hover:bg-[var(--wraith-border)] transition-colors cursor-pointer"
+            @click="emit('reject')"
+          >
+            Reject
+          </button>
+          <button
+            class="px-4 py-1.5 text-xs rounded transition-colors cursor-pointer"
+            :class="
+              isChanged
+                ? 'bg-[var(--wraith-accent-red)] text-white hover:bg-red-600'
+                : 'bg-[var(--wraith-accent-blue)] text-white hover:bg-blue-600'
+            "
+            @click="emit('accept')"
+          >
+            {{ isChanged ? 'Accept Anyway' : 'Accept' }}
+          </button>
+        </div>
+      </div>
+    </div>
+  </Teleport>
+</template>
+
+<script setup lang="ts">
+defineProps<{
+  hostname: string;
+  keyType: string;
+  fingerprint: string;
+  isChanged: boolean;
+}>();
+
+const emit = defineEmits<{
+  accept: [];
+  reject: [];
+}>();
+</script>
diff --git a/frontend/src/components/sidebar/ConnectionTree.vue b/frontend/src/components/sidebar/ConnectionTree.vue
index 734ca11..ba925f8 100644
--- a/frontend/src/components/sidebar/ConnectionTree.vue
+++ b/frontend/src/components/sidebar/ConnectionTree.vue
@@ -41,6 +41,7 @@
             v-for="conn in connectionStore.connectionsByGroup(group.id)"
             :key="conn.id"
             class="w-full flex items-center gap-2 pl-8 pr-3 py-1.5 text-xs hover:bg-[var(--wraith-bg-tertiary)] transition-colors cursor-pointer"
+            @dblclick="handleConnect(conn)"
           >
             <!-- Protocol dot -->
             <span
@@ -64,9 +65,11 @@
 
 <script setup lang="ts">
 import { ref } from "vue";
-import { useConnectionStore } from "@/stores/connection.store";
+import { useConnectionStore, type Connection } from "@/stores/connection.store";
+import { useSessionStore } from "@/stores/session.store";
 
 const connectionStore = useConnectionStore();
+const sessionStore = useSessionStore();
 
 // All groups expanded by default
 const expandedGroups = ref<Set<number>>(
@@ -80,4 +83,9 @@ function toggleGroup(groupId: number): void {
     expandedGroups.value.add(groupId);
   }
 }
+
+/** Double-click a connection to open a new session. */
+function handleConnect(conn: Connection): void {
+  sessionStore.connect(conn.id);
+}
 </script>
diff --git a/frontend/src/stores/session.store.ts b/frontend/src/stores/session.store.ts
index 2390e18..6c64b2d 100644
--- a/frontend/src/stores/session.store.ts
+++ b/frontend/src/stores/session.store.ts
@@ -1,5 +1,6 @@
 import { defineStore } from "pinia";
 import { ref, computed } from "vue";
+import { useConnectionStore } from "@/stores/connection.store";
 
 export interface Session {
   id: string;
@@ -17,13 +18,9 @@ export interface Session {
  * For now, mock sessions are used to render the tab bar.
  */
 export const useSessionStore = defineStore("session", () => {
-  const sessions = ref<Session[]>([
-    { id: "s1", connectionId: 1, name: "Asgard", protocol: "ssh", active: true },
-    { id: "s2", connectionId: 2, name: "Docker", protocol: "ssh", active: false },
-    { id: "s3", connectionId: 4, name: "CLT-VMHOST01", protocol: "rdp", active: false },
-  ]);
+  const sessions = ref<Session[]>([]);
 
-  const activeSessionId = ref<string | null>("s1");
+  const activeSessionId = ref<string | null>(null);
 
   const activeSession = computed(() =>
     sessions.value.find((s) => s.id === activeSessionId.value) ?? null,
@@ -61,6 +58,31 @@ export const useSessionStore = defineStore("session", () => {
     activeSessionId.value = id;
   }
 
+  /**
+   * Connect to a server by connection ID.
+   * Creates a new session tab and sets it active.
+   *
+   * TODO: Replace with Wails binding call — SSHService.Connect(hostname, port, ...)
+   * For now, creates a mock session using the connection's name.
+   */
+  function connect(connectionId: number): void {
+    const connectionStore = useConnectionStore();
+    const conn = connectionStore.connections.find((c) => c.id === connectionId);
+    if (!conn) return;
+
+    // Check if there's already an active session for this connection
+    const existing = sessions.value.find((s) => s.connectionId === connectionId);
+    if (existing) {
+      activeSessionId.value = existing.id;
+      return;
+    }
+
+    // TODO: Replace with Wails binding call:
+    //   const sessionId = await SSHService.Connect(conn.hostname, conn.port, username, authMethods, cols, rows)
+    // For now, create a mock session
+    addSession(connectionId, conn.name, conn.protocol);
+  }
+
   return {
     sessions,
     activeSessionId,
@@ -69,5 +91,6 @@ export const useSessionStore = defineStore("session", () => {
     activateSession,
     closeSession,
     addSession,
+    connect,
   };
 });