Purpose. Habits may be a mechanism linking environmental variables with active commuting. This study investigated the role of habit strength in the explanation of active commuting across profiles based on current active commuting, motivation, and habit strength within the framework of the theory of planned behavior (TPB). Design. Cross-sectional survey using validated questionnaires. Setting. Undergraduate students who participated for course credits. Subjects. Five hundred and thirty-eight students (mean age = 21.19 [SD = 2.57]; 28.45% males; response rate = 86.36%). Measures. Questionnaire included TPB items, underlying beliefs, and a validated measure of habit strength. Active commuting was assessed with relevant items from the International Physical Activity Questionnaire. Analysis. Hierarchical regression and interaction analyses, discriminant function analysis, and analyses of variance. Results. Habit strength was the strongest correlate of active commuting and interacted with intention: at low and medium levels of habit strength, the intention–bicycle use relationship was more than twice as strong as at high levels. Beliefs regarding situational barriers were amongst the most discriminating beliefs, whereas beliefs regarding health benefits did not distinguish profiles. Conclusions. Stronger active commuting habits are associated with a lower association between intention and bicycle use. Persuasive health campaigns might more usefully instill a sense of confidence in various commuting situations rather than merely emphasizing health benefits of active commuting. (Am J Health Promot 2011;25[3]:e27–e36.)