diff --git a/PackageDownloader/PackageDownloader.csproj b/PackageDownloader/PackageDownloader.csproj
new file mode 100644
index 00000000..632bf9c7
--- /dev/null
+++ b/PackageDownloader/PackageDownloader.csproj
@@ -0,0 +1,14 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net10.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="NuGet.Versioning" Version="7.9.0" />
+  </ItemGroup>
+
+</Project>
diff --git a/PackageDownloader/Program.cs b/PackageDownloader/Program.cs
new file mode 100644
index 00000000..c7b44a84
--- /dev/null
+++ b/PackageDownloader/Program.cs
@@ -0,0 +1,309 @@
+using System.IO.Compression;
+using System.Text.Json;
+using System.Xml.Linq;
+using NuGet.Versioning;
+
+const string NuGetIndexUrl = "https://packagefeedproxy.microsoft.io/nuget/v3/index.json";
+const string NetCoreRefPackageId = "Microsoft.NETCore.App.Ref";
+const string WindowsDesktopRefPackageId = "Microsoft.WindowsDesktop.App.Ref";
+const string DefaultDotnetDir = @"C:\Users\gewarren\binaries\dotnet";
+const string DefaultMajorVersion = "11.0";
+const string ShimReferencesUrl = "https://raw.githubusercontent.com/dotnet/runtime/v7.0.0-preview.1.22076.8/src/libraries/shims/netfxreference.props";
+
+(Dictionary<string, string> options, string? error) = ParseArguments(args);
+if (error is not null)
+{
+    throw new ArgumentException(error);
+}
+
+string dotnetDir = GetOption(options, "--dotnet-dir", DefaultDotnetDir);
+string majorVersion = GetOption(options, "--version", DefaultMajorVersion);
+string refTargetFramework = $"net{majorVersion}";
+
+using HttpClient httpClient = new();
+httpClient.Timeout = TimeSpan.FromMinutes(5);
+httpClient.DefaultRequestHeaders.UserAgent.ParseAdd("PackageDownloader/1.0");
+
+string downloadDir = Path.Combine(Path.GetTempPath(), "ref-packages");
+ClearDirectory(downloadDir);
+
+string packageBaseAddress = await GetPackageBaseAddressAsync(httpClient);
+HashSet<string> shimDllExclusions = await GetShimDllExclusionsAsync(httpClient);
+HashSet<string> xmlFilesToCopy = BuildFileNameSet(
+    "Microsoft.Extensions.Caching.Abstractions.xml",
+    "Microsoft.Extensions.Configuration.Abstractions.xml",
+    "Microsoft.Extensions.DependencyInjection.Abstractions.xml",
+    "Microsoft.Extensions.Diagnostics.Abstractions.xml",
+    "Microsoft.Extensions.FileProviders.Abstractions.xml",
+    "Microsoft.Extensions.Hosting.Abstractions.xml",
+    "Microsoft.Extensions.Logging.Abstractions.xml",
+    "Microsoft.Extensions.Options.xml",
+    "Microsoft.Extensions.Primitives.xml",
+    "System.Formats.Asn1.xml",
+    "System.Linq.AsyncEnumerable.xml",
+    "System.Net.ServerSentEvents.xml",
+    "System.Reflection.DispatchProxy.xml",
+    "System.Text.RegularExpressions.xml");
+
+// Copy the .NET Core reference assemblies to the target directory.
+string netCoreExtractDir = await DownloadAndExtractLatestPackageAsync(httpClient, packageBaseAddress, NetCoreRefPackageId, downloadDir);
+string netCoreRefDir = GetRefDirectory(netCoreExtractDir, refTargetFramework);
+string netCoreDestination = Path.Combine(dotnetDir, $"net-{majorVersion}");
+
+ClearDirectory(netCoreDestination);
+CopyFiles(netCoreRefDir, netCoreDestination, "*.dll", shimDllExclusions);
+CopyNamedFiles(netCoreRefDir, netCoreDestination, xmlFilesToCopy);
+
+// Copy the Windows Desktop reference assemblies to the target directory.
+string windowsDesktopExtractDir = await DownloadAndExtractLatestPackageAsync(httpClient, packageBaseAddress, WindowsDesktopRefPackageId, downloadDir);
+string windowsDesktopRefDir = GetRefDirectory(windowsDesktopExtractDir, refTargetFramework);
+string windowsDesktopDir = $"windowsdesktop-{majorVersion}";
+string windowsDesktopDestination = Path.Combine(dotnetDir, windowsDesktopDir);
+
+ClearDirectory(windowsDesktopDestination);
+CopyFiles(
+    windowsDesktopRefDir,
+    windowsDesktopDestination,
+    "*.dll",
+    new HashSet<string>(StringComparer.OrdinalIgnoreCase)
+    {
+        "Microsoft.VisualBasic.dll",
+        "System.Drawing.dll"
+    });
+
+// Copy System.Security.Cryptography.dll to the dependencies directory for WindowsDesktop.
+string cryptoSource = Path.Combine(netCoreDestination, "System.Security.Cryptography.dll");
+if (!File.Exists(cryptoSource))
+{
+    throw new FileNotFoundException("Could not find the copied System.Security.Cryptography.dll dependency.", cryptoSource);
+}
+
+string dependenciesDestination = Path.Combine(dotnetDir, "dependencies", windowsDesktopDir);
+Directory.CreateDirectory(dependenciesDestination);
+File.Copy(cryptoSource, Path.Combine(dependenciesDestination, Path.GetFileName(cryptoSource)), overwrite: true);
+Console.WriteLine($"Copied {Path.GetFileName(cryptoSource)} to {dependenciesDestination}.");
+
+#region Helper methods
+static async Task<string> GetPackageBaseAddressAsync(HttpClient httpClient)
+{
+    using JsonDocument serviceIndex = await GetJsonDocumentAsync(httpClient, NuGetIndexUrl);
+
+    foreach (JsonElement resource in serviceIndex.RootElement.GetProperty("resources").EnumerateArray())
+    {
+        if (!resource.TryGetProperty("@type", out JsonElement typeElement) ||
+            !resource.TryGetProperty("@id", out JsonElement idElement))
+        {
+            continue;
+        }
+
+        string? resourceType = typeElement.GetString();
+        string? resourceId = idElement.GetString();
+        if (resourceType?.Contains("PackageBaseAddress/3.0.0", StringComparison.Ordinal) == true &&
+            !string.IsNullOrWhiteSpace(resourceId))
+        {
+            return resourceId.TrimEnd('/') + "/";
+        }
+    }
+
+    throw new InvalidOperationException($"Could not find a PackageBaseAddress resource in {NuGetIndexUrl}.");
+}
+
+static async Task<HashSet<string>> GetShimDllExclusionsAsync(HttpClient httpClient)
+{
+    string propsXml = await httpClient.GetStringAsync(ShimReferencesUrl);
+    XDocument props = XDocument.Parse(propsXml);
+
+    HashSet<string> exclusions = new(StringComparer.OrdinalIgnoreCase);
+    foreach (XElement reference in props.Descendants("NetFxReference"))
+    {
+        string? include = reference.Attribute("Include")?.Value;
+        if (!string.IsNullOrWhiteSpace(include))
+        {
+            exclusions.Add(include + ".dll");
+        }
+    }
+
+    if (exclusions.Count == 0)
+    {
+        throw new InvalidOperationException($"No NetFxReference entries were found in {ShimReferencesUrl}.");
+    }
+
+    return exclusions;
+}
+
+static async Task<string> DownloadAndExtractLatestPackageAsync(
+    HttpClient httpClient,
+    string packageBaseAddress,
+    string packageId,
+    string downloadDir)
+{
+    string packageIdLower = packageId.ToLowerInvariant();
+    string versionsUrl = $"{packageBaseAddress}{packageIdLower}/index.json";
+    using JsonDocument versionsDocument = await GetJsonDocumentAsync(httpClient, versionsUrl);
+
+    List<(string Original, NuGetVersion Parsed)> versions = [];
+    foreach (JsonElement versionElement in versionsDocument.RootElement.GetProperty("versions").EnumerateArray())
+    {
+        string? version = versionElement.GetString();
+        if (string.IsNullOrWhiteSpace(version))
+        {
+            continue;
+        }
+
+        if (!NuGetVersion.TryParse(version, out NuGetVersion? parsedVersion))
+        {
+            throw new InvalidOperationException($"The feed returned an invalid NuGet version for {packageId}: {version}");
+        }
+
+        versions.Add((version, parsedVersion));
+    }
+
+    if (versions.Count == 0)
+    {
+        throw new InvalidOperationException($"No versions were found for {packageId} at {versionsUrl}.");
+    }
+
+    string latestVersion = versions.MaxBy(version => version.Parsed)!.Original;
+    string packageDir = Path.Combine(downloadDir, packageIdLower, latestVersion);
+    Directory.CreateDirectory(packageDir);
+
+    string packagePath = Path.Combine(packageDir, $"{packageIdLower}.{latestVersion}.nupkg");
+    string packageUrl = $"{packageBaseAddress}{packageIdLower}/{latestVersion}/{packageIdLower}.{latestVersion}.nupkg";
+
+    await using (Stream packageStream = await httpClient.GetStreamAsync(packageUrl))
+    await using (FileStream packageFile = File.Create(packagePath))
+    {
+        await packageStream.CopyToAsync(packageFile);
+    }
+
+    string extractDir = Path.Combine(packageDir, "extracted");
+    ClearDirectory(extractDir);
+    ZipFile.ExtractToDirectory(packagePath, extractDir, overwriteFiles: true);
+
+    Console.WriteLine($"Downloaded and extracted {packageId} {latestVersion}.");
+    return extractDir;
+}
+
+static async Task<JsonDocument> GetJsonDocumentAsync(HttpClient httpClient, string url)
+{
+    await using Stream stream = await httpClient.GetStreamAsync(url);
+    return await JsonDocument.ParseAsync(stream);
+}
+
+static string GetRefDirectory(string extractDir, string refTargetFramework)
+{
+    string refRoot = Path.Combine(extractDir, "ref");
+    if (!Directory.Exists(refRoot))
+    {
+        throw new DirectoryNotFoundException($"The package does not contain a ref directory: {extractDir}");
+    }
+
+    string preferredRefDir = Path.Combine(refRoot, refTargetFramework);
+    if (Directory.Exists(preferredRefDir))
+    {
+        return preferredRefDir;
+    }
+
+    string[] candidateDirs = Directory.GetDirectories(refRoot);
+    if (candidateDirs.Length == 1)
+    {
+        return candidateDirs[0];
+    }
+
+    throw new DirectoryNotFoundException($"The package does not contain a ref/{refTargetFramework} directory (and could not infer one) under: {extractDir}");
+}
+
+static (Dictionary<string, string> Options, string? Error) ParseArguments(string[] args)
+{
+    Dictionary<string, string> options = new(StringComparer.OrdinalIgnoreCase);
+    for (int index = 0; index < args.Length; index++)
+    {
+        string option = args[index];
+        if (option is not ("--dotnet-dir" or "--version"))
+        {
+            return (options, $"Unknown option '{option}'. Supported options: --dotnet-dir <path> and --version <major.minor>.");
+        }
+
+        if (index + 1 >= args.Length || args[index + 1].StartsWith("--", StringComparison.Ordinal))
+        {
+            return (options, $"Option '{option}' requires a value.");
+        }
+
+        options[option] = args[++index];
+    }
+
+    return (options, null);
+}
+
+static string GetOption(IReadOnlyDictionary<string, string> options, string name, string defaultValue)
+{
+    return options.TryGetValue(name, out string? value) && !string.IsNullOrWhiteSpace(value)
+        ? value
+        : defaultValue;
+}
+
+static void CopyFiles(string sourceDir, string destinationDir, string searchPattern, ISet<string> excludedFileNames)
+{
+    Directory.CreateDirectory(destinationDir);
+
+    int copiedCount = 0;
+    foreach (string sourcePath in Directory.EnumerateFiles(sourceDir, searchPattern, SearchOption.TopDirectoryOnly))
+    {
+        string fileName = Path.GetFileName(sourcePath);
+        if (excludedFileNames.Contains(fileName))
+        {
+            continue;
+        }
+
+        File.Copy(sourcePath, Path.Combine(destinationDir, fileName), overwrite: true);
+        copiedCount++;
+    }
+
+    Console.WriteLine($"Copied {copiedCount} {searchPattern} files from {sourceDir} to {destinationDir}.");
+}
+
+static void CopyNamedFiles(string sourceDir, string destinationDir, ISet<string> fileNamesToCopy)
+{
+    Directory.CreateDirectory(destinationDir);
+
+    int copiedCount = 0;
+    foreach (string fileName in fileNamesToCopy)
+    {
+        string sourcePath = Path.Combine(sourceDir, fileName);
+        if (!File.Exists(sourcePath))
+        {
+            throw new FileNotFoundException("Could not find an expected XML reference file.", sourcePath);
+        }
+
+        File.Copy(sourcePath, Path.Combine(destinationDir, fileName), overwrite: true);
+        copiedCount++;
+    }
+
+    Console.WriteLine($"Copied {copiedCount} named files from {sourceDir} to {destinationDir}.");
+}
+
+static HashSet<string> BuildFileNameSet(params string[] fileNames)
+{
+    HashSet<string> names = new(StringComparer.OrdinalIgnoreCase);
+    foreach (string fileName in fileNames)
+    {
+        names.Add(fileName);
+        if (Path.GetExtension(fileName).Length == 0)
+        {
+            names.Add(fileName + ".xml");
+        }
+    }
+
+    return names;
+}
+
+static void ClearDirectory(string directory)
+{
+    if (Directory.Exists(directory))
+    {
+        Directory.Delete(directory, recursive: true);
+    }
+
+    Directory.CreateDirectory(directory);
+}
+#endregion
diff --git a/PackageDownloader/README.md b/PackageDownloader/README.md
new file mode 100644
index 00000000..05b6da1d
--- /dev/null
+++ b/PackageDownloader/README.md
@@ -0,0 +1,30 @@
+# PackageDownloader
+
+`PackageDownloader` updates local reference assemblies used to feed the .NET API 
+reference documentation generator. It downloads the latest .NET Core and Windows Desktop 
+reference assemblies from the packages available on the NuGet V3 feed 
+at `https://packagefeedproxy.microsoft.io/nuget/v3/index.json`.
+
+## Run
+
+From the repository root:
+
+```powershell
+dotnet run --project PackageDownloader\PackageDownloader.csproj
+```
+
+Override the output directory and .NET version with named arguments:
+
+```powershell
+dotnet run --project PackageDownloader\PackageDownloader.csproj -- --dotnet-dir C:\Users\me\binaries\dotnet --version 11.0
+```
+
+Options:
+
+- `--dotnet-dir <path>`: root output directory. Defaults to `C:\Users\gewarren\binaries\dotnet`.
+- `--version <major.minor>`: .NET version used to select the package `ref/net<version>` directory and name the output directories. Defaults to `11.0`.
+
+The program deletes and recreates its target output directories, so don't run it
+while files in those directories are being edited or used by another process.
+
+The tool also downloads shim exclusions from the `netfxreference.props` file in dotnet/runtime to decide which assemblies to skip.