The men's decathlon at the 2009 World Championships in Athletics was held at the Olympic Stadium on August 19 and August 20.
The competition is notable for having the highest number of competitors (38) and the highest proportion of athletes (almost 89.5 %) finishing the competition in the World Championships history.
Prior to the competition, the following records were as follows.
Key: PB = Personal best, SB = Seasonal best, WL = World leading (in a given season)