Diversity is an integral part of today's business environment. This thesis examines the role of diversity in Australian corporate governance. Specifically, the thesis aims to theoretically understand diversity within the context of Australian boards, to further develop measures of diversity, to describe the extent of diversity on Australian boards, to examine the impact of board diversity under various governance theories, and to determine if diversity directly impacts firm performance. A different approach to previous research is taken, merging psychological theories of diversity with mainstream corporate governance theories. The thesis examines the top 100 companies listed on the Australian Stock Exchange (ASX) in 1999. These companies are an important economic force, accounting for roughly 85% of revenue, assets, and market capitalisation listed on the ASX. Hierarchical multiple regression is used to test hypotheses. The thesis finds that diversity impacts board outcomes in a manner consistent with corporate governance theories, but fails to directly impact firm performance. The main theoretical contributions of the thesis are the merging of psychological diversity and corporate governance theories, the application of corporate governance theories to diversity, and the development of new measurement approaches to studying diversity. The main contribution to practice is knowledge about the level and impact of diversity in Australian boards.