The Czech Republic National Basketball League (NBL) (in Czech: Národní Basketbalová Liga), also called the Mattoni NBL for sponsorship reasons, is the top level professional basketball league in the Czech Republic. The league operates under a promotion and relegation system. The bottom two NBL teams from each season's standings are relegated to the 1. Liga, while the top two 1. Liga teams from each season's standings are promoted to the NBL. The league is sponsored by Mattoni, a brand of mineral water.