Metaphors are pervasive in both mass communication and interpersonal exchanges and can play an important role in persuasion. Metaphor serves multiple functions in persuasive communication, and the effect of metaphor on persuasion is potentially mediated by multiple psychological process mechanisms. Nevertheless, we propose that past and future research in this area can be organized or grouped into three simple categories. First, metaphorical statements can activate information that is directly applied to the communication topic and thereby influence attitudes toward the communication topic. Second, metaphorical language may influence impressions of the communication source and thereby impact attitudes toward the communication topic. Third, metaphors may affect attitudes toward the communication topic by influencing the direction or amount of elaboration that takes place when recipients process literal statements contained in the communication. A review of past research is organized into these three categories, and proposals for future research in each category are introduced. It is concluded that future research within each of these domains should focus on two related questions: under what conditions does metaphor elicit a given psychological process in the receiver (e.g., attribute mapping, valence transfer), and under what conditions will a given process result in an increase versus decrease in persuasion?