This thesis examines the effect of team gender diversity on team functioning. Whilst both theoretically and empirically there is considerable support for the proposition that gender diversity will affect team functioning, past research does not provide a coherent body of observed findings. Reviewing the literature does however suggest the possibility that the conflicting pattern of findings might be due to several contingency factors. This thesis therefore also explored the possibility of differential effects across gender, type of team and organisational context. Cross-sectional questionnaire based studies were conducted in three very different organisational contexts: a male dominated manufacturing industry, a female dominated health service, and a gender balanced local government housing department. Taken in combination the results of the three studies provided strong support for the proposition that gender diversity is associated with perceptions of team functioning. However, the relationship was not found to be straightforward. Firstly, a differential effect of team gender diversity on men and women was found. Secondly, it was shown that the effects of team gender diversity were greater within management than non-management teams. Finally, although gender diversity was found to affect perceptions of team functioning within all three studies, the nature and magnitude of the effects was found to be dependant upon the organisational context. Within gender skewed contexts (i.e. male dominated or female dominated contexts) a token representation of the minority was found to be particularly detrimental to perceptions of team functioning. However, once the proportion of women in the team exceeded tokenism, greater gender diversity was found to be beneficial to the team. In contrast, in the gender balanced context diversity per se was not found to effect team functioning, rather the presence of women in particular created better team functioning.