Therapists' cognitive complexity can influence a variety of clinical and educational processes, from how they make decisions to their engagement in classes and supervision. To date, cognitive complexity models have not been adapted or advanced to meet the demands of clinical training. We provide a review and critique of the current cognitive complexity models and examine the measures typically associated with these models. We also introduce a new model, the Therapists' Cognitive Complexity Model, which includes three components of therapists' cognitive complexity: session thoughts, metacognition, and epistemic cognitions. Implications for therapist training and suggestions for future research are provided.