Xamarin.Forms Navigation Syntax

Following GettingStarted of xamarin forms and this code has me in a fix.

listView.ItemSelected += async (sender, e) => {
var todoItem = (TodoItem)e.SelectedItem;
var todoPage = new TodoItemPage(todoItem); // so the new page shows correct data
await Navigation.PushAsync(todoPage);
};

I cannot find "Navigation" in any intellisense.What's wrong here? the namespace i have included is Xamarin.Forms.
Any ideas?