This paper considers why gender mainstreaming (GM), a strategy that many have claimed holds promise for transforming public policy and working towards social justice, is inherently limited and flawed. The paper begins with a brief overview of GM, specifically focusing on the Canadian context, and highlights current discussions in the literature regarding issues of implementation and best practices. It then moves on to reveal that a critical but overlooked dimension of GM is its theoretical foundation. In contextualizing GM within a contemporary feminist theory framework, the paper seeks to illuminate the problematic relationship that currently exists between GM and feminist theory and, moreover, demonstrates why the theoretical premises of GM need significant reworking. The argument put forward is that if insights of recent feminist theorizing are taken seriously, it becomes clear that GM should be replaced by an alternative and broader strategy of diversity mainstreaming. Through the use of practical examples, the paper illustrates how diversity mainstreaming is able to better capture, articulate and make visible the relationship between simultaneously interlocking forms of oppressions that include but are not limited to gender. © 2005 Canadian Political Science Association.