A candidate for political office has private information about his and his rival’s qualifications. A more informative positive (negative) campaign generates a more accurate public signal about his own (his rival’s) qualifications, but costs more. A high type candidate has a comparative advantage in negative campaigns if, relative to the low type, he can lower the voter’s belief about his rival more effectively than he can raise her belief about himself and vice versa. In equilibrium, this comparative advantage determines whether the high type chooses a positive or negative campaign. Further, competition helps the high type separate.