Chapter 6 addresses the question of how advertising influences buying behaviour. Early social psychologists assumed that behaviour was determined by attitudes. When studies showed that behaviour sometimes was, but also sometimes was not related to attitudes, it became clear that the question to ask was not whether, but when attitudes predict behaviour. One of the most important conditions determining when measures of attitudes predict behaviour is compatibility, achieved by either aggregating measures of behaviour to the level of generality of the attitude measure or by making the attitude measure so specific as to apply to the specific behaviour. Prediction of specific behaviour was further improved with the development of the theory of planned behaviour. It assumes that specific behaviour is influenced by attitudes towards that behaviour, social norms and perceived behavioural control. The integration of goal theoretical ideas into that model finally led to the theory of reasoned goal pursuit. But by focusing on processes of deliberate, conscious information processing and decision-making, research has neglected automatic and unconscious processes likely to exert a powerful impact on consumer behaviour. In the mid 1990s, consumer research became aware of this omission in its theorizing and devoted substantial attention to unconscious influences on consumer thoughts, feelings and actions. This research will be reviewed in the second part of this chapter.