Habits involve a direct cue-behavior association in memory. When encountered, cues activate a single, specific well-learned behavioral response. Habits are acquired as a consequence of a history of cue-contingent behavioral repetition. Evidence shows that established habits are cue-contingent, share features of automaticity, and are goal- or reward-independent. Habit cues are readily detected in the environment, associated with short response latencies in computerized tasks and cause “action slips.” Habits are automatic in the sense that cues automatically activate habituated actions without reference to reflective processes. While habits may sometimes be acquired during deliberate goal pursuit, and continue to service goals, once established, cues will prompt behavior irrespective of current motivational state. Habit formation offers an important avenue for development of sustained behavior change interventions. Unlike motivational models of behavior change, habit formation has the potential to create sustained behavior change. Considerable progress has been made in delineating features of habit formation, particularly planning cue-action contingencies and ensuring repetition. Interventions that demonstrate the long-term superiority of habit interventions versus motivational interventions in promoting sustained behavior change require extended behavioral follow-up. Undesired habits share the same attributes as desired habits, so that undoing undesired habits represents a significant challenge for the science of behavior change.