The Commonwealth of nations comprises 54 countries, some of which were part of the British Empire when it existed. The nations join voluntarily and have to commit to common aims, like peace, democracy and human rights. It faces some criticism, with some people calling it Empire 2.0, but others argue its voluntary nature means it's different. The Queen is currently the head of the Commonwealth, and her son Charles is set to take over. But it's not necessarily always going to be the way that the British monarch is the head - the new head is voted for by the members.