Throughout history, men have tended to be more violent than women. Evolutionary theories suggest that this sex difference derives in part from their historically greater need to compete with other men over access to potential mates. In the current research, men and women (Experiment 1) or men only (Experiments 2 and 3) underwent a mating motive prime or control prime, and then performed a task designed to measure aggression toward a same-sex partner. The mating prime increased aggression among men, but not women (Experiment 1). Furthermore, mating-related increases in aggression were directed only toward men who were depicted as viable intrasexual rivals, including a dominant (vs. non-dominant) male partner (Experiment 2) and a man who was depicted as single (versus married) and looking for a mate (Experiment 3). This research provides a picture of male intrasexual aggression as highly selective and aimed strategically at asserting one’s dominance over sexual rivals.