This chapter examines the psychological processes involved in effective persuasion campaigns. It explores concepts of attitude, belief, and behaviour, and analyses the relations between them. The chapter focuses on two general strategies of persuasion–namely, the use of rewards or incentives to change attitudes and the use of persuasive argumentation. People can express their attitudes in various ways, through their cognitions, affects, and behaviours. Several algebraic models attempt to describe precisely the relation between attitudes and beliefs. If attitudes influence overt behaviour, people with positive attitudes towards a given attitude object should engage in behaviours that approach, support and those with negative attitudes should engage in behaviours that avoid, oppose, or hinder the object. From a psychometric perspective, much of the variation in attitude-behaviour correlations can be understood in terms of the reliability and validity of an investigator’s measures of behaviour. The study of incentive-based persuasion concerns the extent to which attitudes and behaviour can be influenced by rewards and punishments.