Tied to essential shortcuts in thinking, cognitive and affective biases function outside of conscious awareness and are known to affect clinical assessment, reasoning, and decision making in general medicine. This article shows how these biases can also impact psychotherapists’ thinking and influence how they conduct psychotherapy, affecting assessment, formulation, and psychotherapeutic practices. Common biases, as described by Tversky, Kahneman, and others include anchoring, ascertainment, availability, base-rate neglect, commission, confirmation, framing, fundamental attribution error, omission, overconfidence, premature closure, sunk costs, and visceral reaction biases. Since these biases can adversely effect psychotherapy processes and outcomes, we present several strategies by which trainees, experienced clinicians and educators can identify their presence and mitigate their harms.