diff --git a/src/TeamsISO.Engine/Controller/IIsoController.cs b/src/TeamsISO.Engine/Controller/IIsoController.cs
new file mode 100644
index 0000000..384f976
--- /dev/null
+++ b/src/TeamsISO.Engine/Controller/IIsoController.cs
@@ -0,0 +1,34 @@
+using TeamsISO.Engine.Domain;
+
+namespace TeamsISO.Engine.Controller;
+
+/// <summary>
+/// Top-of-engine API the WPF host (Phase C) and any future control APIs (OSC / WebSocket in v2.0)
+/// bind to. All commands are async and cancellable.
+/// </summary>
+public interface IIsoController : IAsyncDisposable
+{
+    /// <summary>Observable list of currently-known meeting participants.</summary>
+    IObservable<IReadOnlyList<Participant>> Participants { get; }
+
+    /// <summary>Observable stream of engine alerts (for UI banner display and ops logging).</summary>
+    IObservable<EngineAlert> Alerts { get; }
+
+    /// <summary>Current global processing settings.</summary>
+    FrameProcessingSettings GlobalSettings { get; }
+
+    /// <summary>Starts discovery and supervises the runtime probe. Returns once startup is complete.</summary>
+    Task StartAsync(CancellationToken cancellationToken);
+
+    /// <summary>Returns the latest <see cref="IsoHealthStats"/> for a given participant's ISO, or empty if none.</summary>
+    IsoHealthStats GetStats(Guid participantId);
+
+    /// <summary>Enables an ISO pipeline for the given participant.</summary>
+    Task EnableIsoAsync(Guid participantId, string? customName, CancellationToken cancellationToken);
+
+    /// <summary>Disables and tears down the pipeline for the given participant.</summary>
+    Task DisableIsoAsync(Guid participantId, CancellationToken cancellationToken);
+
+    /// <summary>Updates global processing settings and persists them. Currently does not restart running pipelines (Phase C wires that).</summary>
+    Task SetGlobalSettingsAsync(FrameProcessingSettings settings, CancellationToken cancellationToken);
+}
diff --git a/src/TeamsISO.Engine/Controller/IsoController.cs b/src/TeamsISO.Engine/Controller/IsoController.cs
new file mode 100644
index 0000000..be26051
--- /dev/null
+++ b/src/TeamsISO.Engine/Controller/IsoController.cs
@@ -0,0 +1,205 @@
+using System.Reactive.Linq;
+using System.Reactive.Subjects;
+using System.Threading.Channels;
+using Microsoft.Extensions.Logging;
+using TeamsISO.Engine.Discovery;
+using TeamsISO.Engine.Domain;
+using TeamsISO.Engine.Interop;
+using TeamsISO.Engine.Persistence;
+using TeamsISO.Engine.Pipeline;
+
+namespace TeamsISO.Engine.Controller;
+
+/// <summary>
+/// Default implementation of <see cref="IIsoController"/>.
+/// Holds the participant tracker, the discovery service, the pipeline dictionary, the config store,
+/// and the runtime probe. Exposes participant and alert observables for the host UI.
+/// </summary>
+public sealed class IsoController : IIsoController
+{
+    private readonly INdiInterop _interop;
+    private readonly Func<IsoPipelineConfig, IsoPipeline> _pipelineFactory;
+    private readonly ConfigStore _configStore;
+    private readonly NdiRuntimeProbe _runtimeProbe;
+    private readonly ILogger<IsoController> _logger;
+    private readonly TimeSpan _renameWindow;
+    private readonly TimeSpan _discoveryInterval;
+
+    private readonly ParticipantTracker _tracker;
+    private readonly Channel<DiscoveryEvent> _discoveryChannel;
+    private readonly NdiDiscoveryService _discovery;
+    private readonly Dictionary<Guid, IsoPipeline> _pipelines = new();
+    private readonly BehaviorSubject<IReadOnlyList<Participant>> _participants =
+        new(Array.Empty<Participant>());
+    private readonly Subject<EngineAlert> _alerts = new();
+    private readonly object _gate = new();
+
+    private FrameProcessingSettings _settings;
+    private CancellationTokenSource? _cts;
+    private Task? _discoveryTask;
+    private Task? _eventPumpTask;
+
+    public IObservable<IReadOnlyList<Participant>> Participants => _participants.AsObservable();
+    public IObservable<EngineAlert> Alerts => _alerts.AsObservable();
+    public FrameProcessingSettings GlobalSettings { get { lock (_gate) return _settings; } }
+
+    public IsoController(
+        INdiInterop interop,
+        Func<IsoPipelineConfig, IsoPipeline> pipelineFactory,
+        ConfigStore configStore,
+        NdiRuntimeProbe runtimeProbe,
+        ILoggerFactory loggerFactory,
+        TimeSpan? renameWindow = null,
+        TimeSpan? discoveryInterval = null,
+        Func<DateTimeOffset>? clock = null)
+    {
+        _interop = interop;
+        _pipelineFactory = pipelineFactory;
+        _configStore = configStore;
+        _runtimeProbe = runtimeProbe;
+        _logger = loggerFactory.CreateLogger<IsoController>();
+        _renameWindow = renameWindow ?? TimeSpan.FromSeconds(5);
+        _discoveryInterval = discoveryInterval ?? TimeSpan.FromMilliseconds(500);
+
+        var loaded = configStore.Load();
+        _settings = loaded.Global;
+
+        _tracker = new ParticipantTracker(_renameWindow, clock ?? (() => DateTimeOffset.UtcNow));
+        _discoveryChannel = Channel.CreateUnbounded<DiscoveryEvent>();
+        _discovery = new NdiDiscoveryService(
+            interop, _discoveryChannel.Writer,
+            loggerFactory.CreateLogger<NdiDiscoveryService>());
+    }
+
+    public async Task StartAsync(CancellationToken cancellationToken)
+    {
+        if (_cts is not null)
+            throw new InvalidOperationException("Controller already started.");
+        _cts = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken);
+
+        // Runtime probe — surface alert if mismatch but don't fail startup.
+        var probeResult = _runtimeProbe.Probe();
+        if (probeResult is NdiRuntimeProbeResult.Mismatch mismatch)
+        {
+            _alerts.OnNext(new EngineAlert.NdiRuntimeMismatch(mismatch.Detected, mismatch.Expected));
+            _logger.LogWarning("NDI runtime mismatch: detected {Detected}, expected {Expected}.",
+                mismatch.Detected, mismatch.Expected);
+        }
+
+        _discoveryTask = _discovery.RunAsync(_discoveryInterval, _cts.Token);
+        _eventPumpTask = PumpDiscoveryEventsAsync(_cts.Token);
+        await Task.CompletedTask;
+    }
+
+    public IsoHealthStats GetStats(Guid participantId)
+    {
+        lock (_gate)
+        {
+            return _pipelines.TryGetValue(participantId, out var pipeline)
+                ? IsoHealthStats.Empty // production wires pipeline.Stats; Phase B-1 leaves this stub
+                : IsoHealthStats.Empty;
+        }
+    }
+
+    public async Task EnableIsoAsync(Guid participantId, string? customName, CancellationToken cancellationToken)
+    {
+        Participant? p;
+        lock (_gate)
+        {
+            if (_pipelines.ContainsKey(participantId)) return;
+            p = _tracker.Participants.FirstOrDefault(x => x.Id == participantId);
+        }
+        if (p is null || p.CurrentSource is null)
+            throw new InvalidOperationException($"Participant {participantId} not currently visible on the network.");
+
+        var output = customName ?? DefaultOutputName(participantId);
+        var config = new IsoPipelineConfig(participantId, p.CurrentSource.FullName, output, _settings);
+        var pipeline = _pipelineFactory(config);
+
+        lock (_gate) _pipelines[participantId] = pipeline;
+        await pipeline.StartAsync();
+        await PersistAssignmentsAsync(cancellationToken);
+    }
+
+    public async Task DisableIsoAsync(Guid participantId, CancellationToken cancellationToken)
+    {
+        IsoPipeline? pipeline;
+        lock (_gate)
+        {
+            if (!_pipelines.Remove(participantId, out pipeline)) return;
+        }
+        await pipeline.StopAsync();
+        await pipeline.DisposeAsync();
+        await PersistAssignmentsAsync(cancellationToken);
+    }
+
+    public Task SetGlobalSettingsAsync(FrameProcessingSettings settings, CancellationToken cancellationToken)
+    {
+        lock (_gate) _settings = settings;
+        return PersistAssignmentsAsync(cancellationToken);
+    }
+
+    private Task PersistAssignmentsAsync(CancellationToken cancellationToken)
+    {
+        try
+        {
+            FrameProcessingSettings settings;
+            IReadOnlyList<IsoAssignment> assignments;
+            lock (_gate)
+            {
+                settings = _settings;
+                assignments = _pipelines.Keys.Select(id =>
+                    new IsoAssignment(id, IsEnabled: true, CustomOutputName: null)).ToArray();
+            }
+            _configStore.Save(new EngineConfig(settings, assignments));
+        }
+        catch (Exception ex)
+        {
+            _alerts.OnNext(new EngineAlert.ConfigSaveFailed(ex.Message));
+            _logger.LogWarning(ex, "Failed to persist engine config.");
+        }
+        return Task.CompletedTask;
+    }
+
+    private async Task PumpDiscoveryEventsAsync(CancellationToken cancellationToken)
+    {
+        try
+        {
+            await foreach (var ev in _discoveryChannel.Reader.ReadAllAsync(cancellationToken))
+            {
+                lock (_gate)
+                {
+                    _tracker.Apply(ev);
+                    _participants.OnNext(_tracker.Participants);
+                }
+            }
+        }
+        catch (OperationCanceledException) { }
+    }
+
+    private static string DefaultOutputName(Guid participantId) =>
+        $"TEAMSISO_{participantId.ToString("N")[..8].ToUpperInvariant()}";
+
+    public async ValueTask DisposeAsync()
+    {
+        _cts?.Cancel();
+        if (_eventPumpTask is not null)
+        {
+            try { await _eventPumpTask; } catch { /* swallow */ }
+        }
+        if (_discoveryTask is not null)
+        {
+            try { await _discoveryTask; } catch { /* swallow */ }
+        }
+        IsoPipeline[] toDispose;
+        lock (_gate)
+        {
+            toDispose = _pipelines.Values.ToArray();
+            _pipelines.Clear();
+        }
+        foreach (var p in toDispose) await p.DisposeAsync();
+        _alerts.OnCompleted();
+        _participants.OnCompleted();
+        _cts?.Dispose();
+    }
+}
diff --git a/src/tests/TeamsISO.Engine.Tests/Controller/IsoControllerTests.cs b/src/tests/TeamsISO.Engine.Tests/Controller/IsoControllerTests.cs
new file mode 100644
index 0000000..cd2d165
--- /dev/null
+++ b/src/tests/TeamsISO.Engine.Tests/Controller/IsoControllerTests.cs
@@ -0,0 +1,145 @@
+using System.Reactive.Linq;
+using Microsoft.Extensions.Logging.Abstractions;
+using TeamsISO.Engine.Controller;
+using TeamsISO.Engine.Domain;
+using TeamsISO.Engine.Interop;
+using TeamsISO.Engine.Persistence;
+using TeamsISO.Engine.Pipeline;
+using TeamsISO.Engine.Tests.Fakes;
+
+namespace TeamsISO.Engine.Tests.Controller;
+
+public class IsoControllerTests : IDisposable
+{
+    private readonly string _dir;
+    private readonly ConfigStore _store;
+    private readonly FakeNdiInterop _interop;
+    private readonly NdiRuntimeProbe _probeMatch;
+    private readonly NdiRuntimeProbe _probeMismatch;
+    private readonly List<IsoPipelineConfig> _factoryCalls = new();
+    private readonly Dictionary<Guid, TaskCompletionSource> _pipelineBlockers = new();
+
+    public IsoControllerTests()
+    {
+        _dir = Path.Combine(Path.GetTempPath(), $"teamsiso-controller-{Guid.NewGuid():N}");
+        Directory.CreateDirectory(_dir);
+        _store = new ConfigStore(Path.Combine(_dir, "config.json"), NullLogger<ConfigStore>.Instance);
+        _interop = new FakeNdiInterop { RuntimeVersion = "6.0.0" };
+        _probeMatch = new NdiRuntimeProbe(_interop, expectedVersion: "6.0.0");
+        _probeMismatch = new NdiRuntimeProbe(_interop, expectedVersion: "9.9.9");
+    }
+
+    public void Dispose() => Directory.Delete(_dir, recursive: true);
+
+    private IsoPipeline TestPipelineFactory(IsoPipelineConfig config)
+    {
+        _factoryCalls.Add(config);
+        var blocker = new TaskCompletionSource();
+        _pipelineBlockers[config.ParticipantId] = blocker;
+        var backoff = new ExponentialBackoff(maxAttempts: 3, initial: TimeSpan.FromMilliseconds(1), cap: TimeSpan.FromMilliseconds(5));
+        return new IsoPipeline(
+            config.ParticipantId,
+            ct => blocker.Task.WaitAsync(ct),
+            backoff,
+            (_, _) => Task.CompletedTask,
+            NullLoggerFactory.Instance);
+    }
+
+    private IsoController NewController(NdiRuntimeProbe? probe = null) =>
+        new(
+            _interop,
+            TestPipelineFactory,
+            _store,
+            probe ?? _probeMatch,
+            NullLoggerFactory.Instance,
+            renameWindow: TimeSpan.FromSeconds(5),
+            discoveryInterval: TimeSpan.FromMilliseconds(20));
+
+    [Fact]
+    public async Task DiscoveredParticipant_AppearsInParticipantsObservable()
+    {
+        await using var controller = NewController();
+        var seenLists = new List<IReadOnlyList<Participant>>();
+        using var sub = controller.Participants.Subscribe(p => seenLists.Add(p));
+
+        await controller.StartAsync(CancellationToken.None);
+        _interop.Sources.Add("PC1 (Teams - Jane)");
+
+        // Wait for discovery to pick it up
+        var deadline = DateTime.UtcNow.AddSeconds(2);
+        while (seenLists.LastOrDefault()?.Any() != true && DateTime.UtcNow < deadline)
+            await Task.Delay(20);
+
+        seenLists.Last().Should().HaveCount(1);
+        seenLists.Last()[0].DisplayName.Should().Be("Jane");
+    }
+
+    [Fact]
+    public async Task EnableIsoAsync_CreatesAndStartsPipeline()
+    {
+        await using var controller = NewController();
+        await controller.StartAsync(CancellationToken.None);
+
+        _interop.Sources.Add("PC1 (Teams - Jane)");
+        var pid = await WaitForFirstParticipantAsync(controller);
+
+        await controller.EnableIsoAsync(pid, customName: "TEAMSISO_JANE", CancellationToken.None);
+
+        _factoryCalls.Should().HaveCount(1);
+        _factoryCalls[0].OutputName.Should().Be("TEAMSISO_JANE");
+        _factoryCalls[0].SourceName.Should().Be("PC1 (Teams - Jane)");
+    }
+
+    [Fact]
+    public async Task DisableIsoAsync_StopsPipeline_AndRemovesIt()
+    {
+        await using var controller = NewController();
+        await controller.StartAsync(CancellationToken.None);
+
+        _interop.Sources.Add("PC1 (Teams - Jane)");
+        var pid = await WaitForFirstParticipantAsync(controller);
+        await controller.EnableIsoAsync(pid, customName: null, CancellationToken.None);
+
+        // Unblock the pipeline so StopAsync can complete
+        _pipelineBlockers[pid].SetResult();
+        await controller.DisableIsoAsync(pid, CancellationToken.None);
+
+        // Re-enable should now create a new pipeline
+        await controller.EnableIsoAsync(pid, customName: null, CancellationToken.None);
+        _factoryCalls.Should().HaveCount(2);
+    }
+
+    [Fact]
+    public async Task SetGlobalSettingsAsync_PersistsToConfigStore()
+    {
+        await using var controller = NewController();
+        var newSettings = new FrameProcessingSettings(
+            TargetFramerate.Fps59_94, TargetResolution.R1080p, AspectMode.Pillarbox, AudioMode.Auto);
+
+        await controller.SetGlobalSettingsAsync(newSettings, CancellationToken.None);
+
+        controller.GlobalSettings.Should().Be(newSettings);
+        _store.Load().Global.Should().Be(newSettings);
+    }
+
+    [Fact]
+    public async Task StartAsync_RuntimeProbeMismatch_RaisesAlert()
+    {
+        await using var controller = NewController(probe: _probeMismatch);
+        var alerts = new List<EngineAlert>();
+        using var sub = controller.Alerts.Subscribe(alerts.Add);
+
+        await controller.StartAsync(CancellationToken.None);
+
+        alerts.Should().Contain(a => a is EngineAlert.NdiRuntimeMismatch);
+    }
+
+    private static async Task<Guid> WaitForFirstParticipantAsync(IsoController controller)
+    {
+        var tcs = new TaskCompletionSource<Guid>();
+        using var sub = controller.Participants
+            .Where(p => p.Count > 0)
+            .Subscribe(p => tcs.TrySetResult(p[0].Id));
+        return await tcs.Task.WaitAsync(TimeSpan.FromSeconds(3));
+    }
+}