Advanced democracies' defence and security forces have the privileged task of upholding the democratic way of life and its underlying values. Why, then, are they increasingly unrepresentative of the societies they allegedly serve? These organisations widely see diversity as a liability. They appear to have good reasons to defend their reticence. Contra the prevailing logic, this article posits diversity as a strategic asset. However, rather than relying on normative theoretical claims, the article defends the merits of diversity in the security and defence sectors on functional grounds. Operational, demographic, economic, formal-constitutional, and political trends militate for a paradigm shift: diversity's payoffs for the organisations' functional imperative greatly outweigh perceived costs. © 2009 Taylor & Francis.