Therapists' use of metaphor in psychotherapy is ubiquitous. However, compared to theoretical and clinical claims about the potential effectiveness of using metaphor, research investigations pose challenges and remain relatively sparse. We provide examples of metaphors in sessions and then systematically review the empirical literature. This research suggests that collaborative coelaboration of metaphors with clients is related to positive in-session client outcomes, particularly cognitive engagement. Future research might benefit from a more in-depth focus on the process and impacts of using metaphors. We draw out implications from the research for clinical training and psychotherapy practice. Clinical Impact Statement Question: Psychotherapists and their clients often use conventional metaphors (e.g., "You seem down today") and, on occasion, novel metaphors (e.g., "I stab people with my voice") over the course of treatment. Here, we review the sparse evidence for the links between metaphors and outcomes. Findings: Tentative links between collaborative coelaboration of metaphors and client cognitive processes such as problem-setting, reflecting, and connecting have been established. Meaning: Collaboratively working with clients to develop metaphors related to major themes of therapy can be an effective intervention. Next Steps: Additional research that brings together therapists, clients, and researchers for in-depth analyses of metaphor use over the course of psychotherapy is needed.