This article contributes a comprehensive model of homework in cognitive behavior therapy (CBT). To this end, several issues in the definition of homework and homework compliance are outlined, research on homework-outcome relations is critiqued, before an overview of classical and operant conditioning along with various cognitive theories are tied together in a comprehensive model. We suggest engagement represents a more clinically meaningful construct than compliance (or adherence). We describe how established behavior and cognitive theories are relevant for understanding patient engagement and what between-session and in-session processes are useful in a comprehensive model. Our primary conclusion from the review of this literature is that current research has focused on limited aspects of homework and missed theoretically meaningful determinants of engagement. Further, little research has sought to examine the role of the therapist in facilitating these theoretically meaningful determinants. The literature on homework is the most advanced of the process research in CBT; the comprehensive model presented here offers clarity for the practicing clinician and represents a testable model for researchers interested in quantifying determinants of homework engagement and the process of integrating homework into CBT.