Rugby league football, commonly known as rugby league in English-speaking countries and rugby XIII in non-Anglophone Europe and South America, and referred to colloquially as rugby, football, footy or league in its heartlands, is a full-contact sport played by two teams of thirteen players on a rectangular field measuring 68 m (74 yd) wide and 112–122 m (122–133 yd) long with H-shaped posts at both ends. It is one of the two major codes of rugby football, the other being rugby union. It originated in 1895 in Huddersfield, Yorkshire, England, as the result of a split from the Rugby Football Union (RFU) over the issue of payments to players. The rules of the game governed by the new Northern Rugby Football Union progressively changed from those of the RFU with the specific aim of producing a faster and more entertaining game to appeal to spectators, on whose income the new organisation and its members depended.

The team sports rugby union and rugby league have shared origins and thus many similarities. Initially, following the 1895 split in rugby football, rugby union and rugby league differed in administration only. Soon, however, the rules of rugby league were modified, resulting in two distinctly different forms of rugby.