Problem definition in program planning and evaluation is rarely problematized. In this article, I discuss why the lack of problem problematization is itself problematic--in other words, why treating problems as self-evident can pose a risk for evaluation practice. Then, to help avoid such risks, I suggest Carol Bacchi's "What's the Problem Represented to Be?" approach as a useful tool to focus evaluative thinking on the frequently tacit step of problem definition. Bacchi's approach, informed by feminist and poststructuralist epistemologies, is designed to facilitate critical interrogation of policies and programs, focusing on the social and value-laden ways in which problems are initially defined. I propose that evaluators can fruitfully use Bacchi's tool to promote evaluative thinking about the assumptions that inhere problem representation and thus can help promote better evaluation.