Among parliamentary democracies there is a widespread belief that above and beyond the occasional opportunity to vote, citizens should be allowed to participate in decisions that affect them. Governments at all levels are now going further and supporting more active forms of citizenship in which various decision processes are open to more public participation. While this principle may be widely accepted, the practice has remained remarkably free from empirical scrutiny. For something that is held to deliver a myriad of benefits, we still know little of the extent to which these are in fact delivered. This article addresses this gap by developing a framework for conducting more robust empirical scrutiny of participatory exercises. It does so at three levels: first by proposing a conceptual clarification of the perceived benefits of greater participation, second by considering some of the methodological challenges in designing more robust evaluative studies and finally by reviewing measures that might be used in practice to quantify benefits.