CreateCompoundIndex.cs

using (var db = Mongo.Create ("mongodb://localhost/testdb"))
	{
		var posts = db.GetCollection<Post> ();
	
                //you can just put a lambda expression in for the fields that you want indexed.
	        posts.CreateIndex (j => new { j.Body, j.Title },
			"Compound_Post_Index",true,IndexOption.Ascending);
	}