The men's 100 metres at the 2005 World Championships in Athletics was held at the Helsinki Olympic Stadium on August 6 and August 7. The top three runners in each of the initial 8 heats automatically qualified for the second round. The next ten fastest runners from across the heats also qualified. Those 32 runners competed in 4 heats in the second round, with the top three runners from each heat and the single next fastest runner qualifying for the semifinals. There were two semifinal heats, and only the top four from each heat advanced to the final.