ContentControl is intended to display a single piece of content. By default, it will stretch to fill its entire containing region, and the content within the ContentControl will stretch to fill it.ItemsControl is intended to display multiple items within it. It will fill its containing region, but the content items added will only take up the space they require. This is because it is intended to allow more than a single item to be added - if the first item stretched to fill up the space, there would be no "room" for the other items added later.