This thesis concerns the need for friendship (called the affiliation motive) and the behaviour that may result from activation of that need. Two major topics are examined; the definition of affiliation and the relationship between joy and affiliation. The problem of defining affiliation arises from a variety of definitions given by various authors, and a consequent variety of tests to measure the affiliation motive. It is suggested that a distinction be made between affiliation, sociability and gregariousness. Affiliation is regarded as a motive for warm, close, friendly relationships, while sociability is regarded as a motive and a skill whose aims are more associative than personal, and gregariousness as non-social behaviour in a social setting. These distinctions are also examined by factor analysis. Two different factor analyses of a variety of questions sorted these questions into three principal categories. These were labelled as an approach affiliation motive, an avoidance affiliation motive and sociability. The dichotomization of the affiliation motive into approach and avoidance aspects is regarded as important in explaining the diverse findings about affiliation. The avoidance motive is concerned with the fear of rejection and possible consequent inhibition of affiliative behaviour. The approach motive is concerned with the expectancy of success in affiliative behaviour. The second topic investigated is the relationship between joy and affiliative behaviour. A series of experiments (based on Schachter's (59) method of analyzing the anxiety~affiliation relationship), manipulated joy and found that as joy increased so did the desire to affiliate. The experiments pointed to self-enhancement and prolongation of joy as being the major determinants of this relationship. Evidence for the generalization of the joy-affiliation is sought in females' reactions to getting engaged and in verbal responses to imagining winning money.