Cognitive and affective biases are essentially connected to heuristic shortcuts in thinking. These biases ordinarily function outside of conscious awareness and potentially affect clinical assessment, reasoning, and decision making in general medicine. However, little consideration has been given to how they may affect clinicians in the conduct of psychotherapy. This article aims to illustrate how such biases may affect assessment, formulation, and conduct of psychotherapy; describe strategies to mitigate these influences; and draw attention to the need for systematic research in this area.Cognitive and affective biases potentially influencing clinical assessment, reasoning, and decision making in medicine were identified in a selective literature review. The authors drew from their experiences as psychotherapists and psychotherapy supervisors to consider how key biases may influence psychotherapists' conduct of psychotherapy sessions.The authors reached consensus in selecting illustrative biases pertinent to psychotherapy. Included biases related to anchoring, ascertainment, availability, base-rate neglect, commission, confirmation, framing, fundamental attribution error, omission, overconfidence, premature closure, sunk costs, and visceral reactions. Vignettes based on the authors' combined experiences are provided to illustrate how these biases could influence the conduct of psychotherapy.Cognitive and affective biases are likely to play important roles in psychotherapy. Clinicians may reduce the potentially deleterious effects of biases by using a variety of mitigating strategies, including education about biases, reflective review, supervision, and feedback. How extensively these biases appear among psychotherapists and across types of psychotherapy and how their adverse effects may be most effectively alleviated to minimize harm deserve systematic study.