Self-Host Web API and Controllers in Class Libraries with Autofac: http://www.codemonkeez.com/2013/04/self-host-web-api-and-controllers-in.html

AutoFacConfig.cs

public class AutoFacConfig
{
    public static void Initialize(HttpConfiguration config)
    {
        Initialize(config, RegisterServices(new ContainerBuilder()));
    }

    public static void Initialize(HttpConfiguration config, IContainer container)
    {
        config.DependencyResolver = new AutofacWebApiDependencyResolver(container);
    }

    private static IContainer RegisterServices(ContainerBuilder builder)
    {
        builder.RegisterApiControllers(Assembly.GetExecutingAssembly());

        // Services
        builder.RegisterType<ProductsController>().InstancePerApiRequest();

        return builder.Build();
    }
}

ProductsController.cs

public class ProductsController : ApiController
{
    Product[] products = new Product[]  
    {  
        new Product { Id = 1, Name = "Tomato Soup", Category = "Groceries", Price = 1 },  
        new Product { Id = 2, Name = "Yo-yo", Category = "Toys", Price = 3.75M },  
        new Product { Id = 3, Name = "Hammer", Category = "Hardware", Price = 16.99M }  
    };

    public IEnumerable<Product> GetAllProducts()
    {
        return products;
    }

    public Product GetProductById(int id)
    {
        var product = products.FirstOrDefault((p) => p.Id == id);
        if (product == null)
        {
            throw new HttpResponseException(HttpStatusCode.NotFound);
        }
        return product;
    }

    public IEnumerable<Product> GetProductsByCategory(string category)
    {
        return products.Where(p => string.Equals(p.Category, category,
                StringComparison.OrdinalIgnoreCase));
    }
}

Program.cs

class Program
{
    static void Main(string[] args)
    {
        var config = new HttpSelfHostConfiguration("http://localhost:8080");

        config.Routes.MapHttpRoute(
            "API Default",
            "api/{controller}/{id}",
            new { id = RouteParameter.Optional }
        );

        AutoFacConfig.Initialize(config);

        using (HttpSelfHostServer server = new HttpSelfHostServer(config))
        {
            server.OpenAsync().Wait();
            System.Console.WriteLine("Press Enter to quit.");
            System.Console.ReadLine();
        }
    }
}