This paper summarizes research on determinants of repeated behaviors, and the decision processes underlying them. The present research focuses on travel mode choices as an example ofsuch behaviors. It is proposed that when behavior is performed repeatedly and becomes habitual, it is guided by automated cognitive processes, rather than being preceded by elaborate decision processes (i.e,, a decision based on attitudes and intentions). First, current attitude-behavior models are discussed, and the role of habit in these models is examined. Second, research is presented on the decision processes preceding travel mode choices. Based on the present theoretical and empirical overview, it is concluded that frequently performed behavior is often a matter of habit, thereby establishing a boundary condition for the applicability of attitude-behavior models. However, more systematic research is required to disentangle the role of habit in attitude-behavior models and to learn more about the cognitive processes underlying habitual behavior.Social psychology is concerned with gaining insight into the psychological antecedents of socially relevant behaviors and the processes underlying them. For instance, on a global level, investigators and practitioners attempt to understand the factors influencing individuals' decisions to engage in behaviors related to health (e.g., smoking, exercising), safety (e.g., following safety instructions at work, using seat belts), and the environment (e.g., recycling, using private cars) in order to prevent, promote, or change these behaviors. Indeed, in the last 25 years, considerable progress has been made in explaining and predicting the initiation of human behaviors as revealed by currently popular attitude-behavior models (e.g., Ajzen,
