diff --git a/Xamarin.MacDev/RuntimeService.cs b/Xamarin.MacDev/RuntimeService.cs
new file mode 100644
index 0000000..cf436d6
--- /dev/null
+++ b/Xamarin.MacDev/RuntimeService.cs
@@ -0,0 +1,94 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT License.
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using Xamarin.MacDev.Models;
+
+#nullable enable
+
+namespace Xamarin.MacDev;
+
+/// <summary>
+/// Manages simulator runtimes via <c>xcrun simctl</c> and <c>xcrun xcodebuild</c>.
+/// </summary>
+public class RuntimeService {
+
+	static readonly string XcrunPath = "/usr/bin/xcrun";
+
+	readonly ICustomLogger log;
+	readonly SimCtl simctl;
+
+	public RuntimeService (ICustomLogger log)
+	{
+		this.log = log ?? throw new ArgumentNullException (nameof (log));
+		simctl = new SimCtl (log);
+	}
+
+	/// <summary>
+	/// Lists installed simulator runtimes. Optionally filters by availability.
+	/// </summary>
+	public List<SimulatorRuntimeInfo> List (bool availableOnly = false)
+	{
+		var json = simctl.Run ("list", "runtimes", "--json");
+		if (json is null)
+			return new List<SimulatorRuntimeInfo> ();
+
+		var runtimes = SimctlOutputParser.ParseRuntimes (json, log);
+
+		if (availableOnly)
+			runtimes.RemoveAll (r => !r.IsAvailable);
+
+		log.LogInfo ("Found {0} simulator runtime(s).", runtimes.Count);
+		return runtimes;
+	}
+
+	/// <summary>
+	/// Lists runtimes for a specific platform (e.g. "iOS", "tvOS", "watchOS", "visionOS").
+	/// </summary>
+	public List<SimulatorRuntimeInfo> ListByPlatform (string platform, bool availableOnly = false)
+	{
+		if (string.IsNullOrEmpty (platform))
+			throw new ArgumentException ("Platform must not be null or empty.", nameof (platform));
+
+		var all = List (availableOnly);
+		return all.Where (r => string.Equals (r.Platform, platform, StringComparison.OrdinalIgnoreCase)).ToList ();
+	}
+
+	/// <summary>
+	/// Downloads a platform runtime using <c>xcrun xcodebuild -downloadPlatform</c>.
+	/// </summary>
+	/// <param name="platform">The platform to download (e.g. "iOS", "tvOS", "watchOS", "visionOS").</param>
+	/// <param name="version">Optional specific version to download (e.g. "17.5").</param>
+	/// <returns>True if the download command succeeded.</returns>
+	public bool DownloadPlatform (string platform, string? version = null)
+	{
+		if (string.IsNullOrEmpty (platform))
+			throw new ArgumentException ("Platform must not be null or empty.", nameof (platform));
+
+		log.LogInfo ("Downloading {0} platform runtime via xcodebuild...", platform);
+
+		try {
+			var args = string.IsNullOrEmpty (version)
+				? new [] { "xcodebuild", "-downloadPlatform", platform }
+				: new [] { "xcodebuild", "-downloadPlatform", platform, "-buildVersion", version! };
+
+			log.LogInfo ("Executing: {0} {1}", XcrunPath, string.Join (" ", args));
+			var (exitCode, _, stderr) = ProcessUtils.Exec (XcrunPath, args);
+			if (exitCode != 0) {
+				log.LogInfo ("xcodebuild -downloadPlatform {0} failed (exit {1}): {2}", platform, exitCode, stderr.Trim ());
+				return false;
+			}
+
+			log.LogInfo ("Successfully downloaded {0} platform runtime.", platform);
+			return true;
+		} catch (System.ComponentModel.Win32Exception ex) {
+			log.LogInfo ("Could not run xcodebuild: {0}", ex.Message);
+			return false;
+		} catch (InvalidOperationException ex) {
+			log.LogInfo ("Could not run xcodebuild: {0}", ex.Message);
+			return false;
+		}
+	}
+}
diff --git a/tests/RuntimeServiceTests.cs b/tests/RuntimeServiceTests.cs
new file mode 100644
index 0000000..1e26988
--- /dev/null
+++ b/tests/RuntimeServiceTests.cs
@@ -0,0 +1,52 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT License.
+
+using System;
+using NUnit.Framework;
+using Xamarin.MacDev;
+
+#nullable enable
+
+namespace tests;
+
+[TestFixture]
+public class RuntimeServiceTests {
+
+	[Test]
+	public void Constructor_ThrowsOnNullLogger ()
+	{
+		Assert.Throws<ArgumentNullException> (() => new RuntimeService (null!));
+	}
+
+	[Test]
+	public void ListByPlatform_ThrowsOnNullPlatform ()
+	{
+		var svc = new RuntimeService (ConsoleLogger.Instance);
+		Assert.Throws<ArgumentException> (() => svc.ListByPlatform (null!));
+		Assert.Throws<ArgumentException> (() => svc.ListByPlatform (""));
+	}
+
+	[Test]
+	public void DownloadPlatform_ThrowsOnNullPlatform ()
+	{
+		var svc = new RuntimeService (ConsoleLogger.Instance);
+		Assert.Throws<ArgumentException> (() => svc.DownloadPlatform (null!));
+		Assert.Throws<ArgumentException> (() => svc.DownloadPlatform (""));
+	}
+
+	[Test]
+	[Platform ("MacOsX")]
+	public void List_DoesNotThrow ()
+	{
+		var svc = new RuntimeService (ConsoleLogger.Instance);
+		Assert.DoesNotThrow (() => svc.List ());
+	}
+
+	[Test]
+	[Platform ("MacOsX")]
+	public void ListByPlatform_DoesNotThrow ()
+	{
+		var svc = new RuntimeService (ConsoleLogger.Instance);
+		Assert.DoesNotThrow (() => svc.ListByPlatform ("iOS"));
+	}
+}