Even through the health benefits of regular exercise and physical activity are well documented, most people are inadequately active or completely inactive.Designing interventions to enhance the adoption and maintenance of a physically active lifestyle continues to be a challenge, given that the majority of individuals are not considering becoming more active, and that over half of those who decide to become more physically active return to a sedentary lifestyle within three to six months.It has been recommended that research on exercise adherence be conducted utilizing models of behavioral science.One of the most effective models is the transtheoretical model of behavior change(TTM).The TTM has been used to explain both the stages and processes people go through when trying to eliminate a negative form of behavior(e.g., smoking)and when trying to acquire a positive form of behavior(e.g., exercise).The model consists of various stages of change, processes of change, decisional balance, and self-efficacy.The TTM suggests that individuals attempting to change exercise behavior move through five stages of change.In addition, individuals experience different congnitive and behavioral processes of change as they move from one stage to another.As people change, decisional balance and self-efficacy are employed uniquely at each stage.According to this model, tailoring interventions to match a person's readiness(stage of change)is essential.Although research on exercise adherence utilizing the TTM has been actively conducted in Western countries, this area of research is yet to be advanced in Japan.This article reviews research on exercise adherence utilizing the TTM, and discusses the applicability of the TTM to understanding physical activity and exercise behavior in the Japanese population.