The sense of humour is a uniquely human skill and understanding humour is an important and rewarding part of social interaction. This thesis begins by discussing the definition of humour, followed by a review of the evidence we have that humour is an evolved and adaptive behaviour. Humour may play an important role in helping individuals to bond and signal cooperation, which may be further communicated by the humour style which is used to communicate. Research has also demonstrated that humour is an attractive quality in a mate, though the precise reasons for this are currently debated (Chapter 1). Empirical work in the first section of the thesis is consistent with evidence demonstrating that humour is attractive and sexually selected for. Chapter 2 tests the influence of modality and relationship context in an effort to further our understanding of why humour is attractive and provides evidence that more attractive people are rated as being funnier than less attractive people. Humour was also found to be more attractive for short-term relationships than long-term relationships, possibly due to the similarity between funniness and flirtatiousness. In Chapter 3, attractiveness ratings of vignettes in the style of personal advertisements, which contained either aggressive or affiliative humour, demonstrated the importance of humour style. An affiliative humour style was more attractive for long-term relationships whereas an aggressive humour style was more attractive for short-term relationships. Further testing provided evidence that humour styles were associated with personality traits which are highly relevant in a mating context, helping to explain the functions of different humour styles. The second section of the thesis examines the relationship between humour, cooperation, and dominance as an alternative explanation for the evolution of humour. Chapter 4 contains an extended introduction to the physical, verbal, and nonverbal cues to dominance and the sex differences that exist in expressive behaviours. Chapter 5 continues this theme and elaborates further on the function of humour in group situations, before providing empirical evidence of how humour is used in the context of a competitive ‘desert-island’ style conversation between same-sex dyads. Chapter 6 further expands on this line of research as empirical evidence presented in this chapter demonstrates that males may be using humour as a way of communicating the desire to cooperate with other males who are of a similar level of dominance. The communication of dominance is further examined in Chapter 7, where ethological evidence showed that males who were more physically dominant tended to knock doors with greater frequency than males who were less physically dominant. In the final chapter of the thesis (Chapter 8), the evolution of humour is discussed in light of the evidence presented in Chapters 2-7. The thesis presents evidence to suggest that humour production is an important skill for males for two reasons. Firstly, a good sense of humour is a highly attractive quality to females and may be a cue to genetic quality or good partner qualities, depending on the humour style used. Secondly, it may be important for males to use humour to signal cooperation to other males in order to form alliances. In females, the evidence presented in the thesis suggests that humour production may be a way for females to demonstrate romantic interest or flirtatiousness but the function of humour use between females remains largely inconclusive.