diff --git a/src/TeamsISO.App/ViewModels/MainViewModel.cs b/src/TeamsISO.App/ViewModels/MainViewModel.cs
new file mode 100644
index 0000000..b7cdfae
--- /dev/null
+++ b/src/TeamsISO.App/ViewModels/MainViewModel.cs
@@ -0,0 +1,96 @@
+using System.Collections.ObjectModel;
+using System.Reactive.Concurrency;
+using System.Reactive.Linq;
+using System.Windows.Threading;
+using TeamsISO.Engine.Controller;
+using TeamsISO.Engine.Domain;
+
+namespace TeamsISO.App.ViewModels;
+
+/// <summary>
+/// Top-level view model for the main window. Owns the live collection of <see cref="ParticipantViewModel"/>,
+/// the global settings panel, and the alert banner. Subscribes to <see cref="IIsoController"/>'s observables
+/// and marshals updates onto the UI dispatcher.
+/// </summary>
+public sealed class MainViewModel : ObservableObject, IDisposable
+{
+    private readonly IIsoController _controller;
+    private readonly Dispatcher _dispatcher;
+    private readonly IDisposable _participantsSub;
+    private readonly IDisposable _alertsSub;
+    private readonly Dictionary<Guid, ParticipantViewModel> _byId = new();
+    private string _statusText = "Starting…";
+
+    public ObservableCollection<ParticipantViewModel> Participants { get; } = new();
+    public GlobalSettingsViewModel Settings { get; }
+    public AlertBannerViewModel AlertBanner { get; } = new();
+
+    public string StatusText
+    {
+        get => _statusText;
+        set => SetField(ref _statusText, value);
+    }
+
+    public MainViewModel(IIsoController controller, Dispatcher dispatcher)
+    {
+        _controller = controller;
+        _dispatcher = dispatcher;
+        Settings = new GlobalSettingsViewModel(controller);
+
+        _participantsSub = controller.Participants
+            .ObserveOn(new SynchronizationContextScheduler(
+                System.Threading.SynchronizationContext.Current ?? new DispatcherSynchronizationContext(_dispatcher)))
+            .Subscribe(OnParticipantsChanged);
+
+        _alertsSub = controller.Alerts
+            .ObserveOn(new SynchronizationContextScheduler(
+                System.Threading.SynchronizationContext.Current ?? new DispatcherSynchronizationContext(_dispatcher)))
+            .Subscribe(alert =>
+            {
+                AlertBanner.Current = alert;
+            });
+    }
+
+    public async Task InitializeAsync(CancellationToken cancellationToken)
+    {
+        StatusText = "Discovering NDI sources…";
+        await _controller.StartAsync(cancellationToken);
+        StatusText = $"Engine running at {_controller.GlobalSettings.FramerateHz:F2} fps target.";
+    }
+
+    private void OnParticipantsChanged(IReadOnlyList<Participant> incoming)
+    {
+        var seenIds = new HashSet<Guid>();
+        foreach (var p in incoming)
+        {
+            seenIds.Add(p.Id);
+            if (_byId.TryGetValue(p.Id, out var vm))
+            {
+                vm.Update(p);
+            }
+            else
+            {
+                vm = new ParticipantViewModel(_controller, p);
+                _byId[p.Id] = vm;
+                Participants.Add(vm);
+            }
+        }
+
+        // Remove participants no longer present
+        for (var i = Participants.Count - 1; i >= 0; i--)
+        {
+            var vm = Participants[i];
+            if (!seenIds.Contains(vm.Id))
+            {
+                _byId.Remove(vm.Id);
+                Participants.RemoveAt(i);
+            }
+        }
+    }
+
+    public void Dispose()
+    {
+        _participantsSub.Dispose();
+        _alertsSub.Dispose();
+    }
+}