Cognitive psychology theories have predominantly been used to examine and understand the determinants of health-related behaviors of the individual, and in particular the role of cognitive factors in predicting behaviors such as smoking, exercise, eating habits, and vaccination adoption. Theories related to motivation, such as social cognitive theory, and the theory of planned behavior; theories related to action, such as implementation intentions theory and the theory of operant conditioning; and theories related to stages of change, such as the transtheoretical model of change have been influential in the field of knowledge translation (KT). This chapter briefly describes the aforementioned theories and their application to KT. Future research in this field should be undertaken using a programmatic approach to systematically and incrementally develop and test theory-based interventions and to validate their theoretical assumptions.