Billennium is a 1961 short story by J.G. Ballard set in a future overpopulated world of around 20 billion people. Most inhabitants live in crowded central cities that charge residents by the square footage of their small living spaces. The story follows two men who discover a secret, larger room and allow friends to share it, but it eventually becomes as crowded as the spaces they wanted to escape. The themes of overcrowding, space shortages, and how people are affected by dense urban living conditions are typical of Ballard's early dystopian works.