England's national under-21 football team, also known as England under-21s or England U21(s), is considered to be the feeder team for the England national football team. This team is for English players aged under 21 at the start of the calendar year in which a two-year European Under-21 Football Championship campaign begins, so some players can remain with the squad until the age of 23. As long as they are eligible, players can play for England at any level, making it possible to play for the U21s, senior side, and again for the U21s, as Jack Butland, Harry Kane, Calum Chambers and John Stones have done. It is also possible to play for one country at youth level and another at senior level (providing the player has not played a senior competitive game in his previous country).