Mainly due to John J. Mearsheimer’s controversial efforts, offensive realism has become a highly visible theory of international politics since the early 1990s. For this reason, he has been called “the leader of the offensive realists.” Accordingly, the present chapter elucidates offensive realism solely through Mearsheimer’s work. Its first section explores the sense in which he regards offensive realism as a realist theory, and defines its main features by contrasting it with Hans Morgenthau’s “human nature realism” and Kenneth Waltz’s “defensive realism.” The second section elucidates offensive realism’s “bedrock assumptions” and their purported “compelling logic.” The subsequent three sections examine Mearsheimer’s attempt to historically validate different aspects of his theory. All five sections conclude that Mearsheimer’s arguments often rest on uncompelling logic and/or are supported with misconstrued historical evidence. This verdict explains, the sixth section argues, the subsequent conversion of his descriptive offensive realism into a predictive approach, which envisions a future world in which the main tenets of offensive realism would materialize. The chapter concludes that its shortcomings and bold assertions explain why Mearsheimer’s offensive realism has remained a high visible but largely unfollowed and controversial restatement of realism.