Rugby union (short for rugby union football) is an outdoor sport played with a spheroid-shaped ball by two teams of 15 players each. It is one of the two main codes of rugby football, the other being rugby league. In both codes, there is also a seven-a-side variant, called rugby sevens, which is played under modified rules and is faster.

Rugby union is often referred to as simply rugby or rugger. It is sometimes known as football, or, in countries where rugby league is also played, as union.