Habit is often treated as a construct of marginal interest in the literature on attitude-behaviour relations. We argue that this is undeserved, particularly given the current interest in principles of automaticity in social psychology. Basic features of habits, such as goal-directed automaticity, their dependency on situational constancy, and functionality, as well as the measurement of habit strength, are discussed. Research is reviewed that contrasted habit with deliberate action, as approached from the theory of planned behaviour, spontaneous vs. deliberate attitude-behaviour processes, implementation intention theory, and decision-making models. Habits thus appear as boundary conditions of the validity of models of planned behaviour and rational decision-making. A habit seems to be accompanied by an enduring cognitive orientation, which we refer to as "habitual mind-set", that makes an individual less attentive to new information and courses of action, and thus contributes to the maintenance of habitual behaviour. Focusing on habitual mind-sets and automatic cue-response links, rather than on statistical associations between past and future behaviour, makes habit an interesting construct for future research.