William Rop Kipsang (born 26 June 1977) is a Kenyan long-distance runner who specialises in the marathon. He has won marathons in Amsterdam, Rotterdam, Beirut and Seoul. His personal best for the event is 2:05:49 hours.His best performance was on 13 April 2008, winning the Rotterdam Marathon with a new course record and PR of 2:05:49. On 15 April 2007 he was placed third in this race, running in difficult circumstances due to the warm weather.