The IAU 50 km World Championships is an annual, global ultrarunning competition over 50 kilometres organized by the International Association of Ultrarunners (IAU). The competition began life as the IAU 50 km World Trophy in 2005. It served as the final leg of the IAU 50 km Challenge circuit, with runners gaining qualification through performances on one of the nine preceding qualifying races. The winners of the men's and women's trophy were decided by the best aggregate time of their World Trophy race plus their best time from the qualifying round. The race moved away from aggregate scoring, with the World Trophy race becoming a straight final, and it continued in this format up to 2014. The 2008 and 2013 editions were cancelled due to the number of world championships the IAU was already