Participation is viewed generally as a positive activity, certainly in the context of democratic societies. Although still contested in some quarters, the idea of stakeholder participation in evaluation is now widely accepted within the evaluation community. Yet the meanings, even the purposes, of stakeholder participation in evaluation remain diverse, multiple, and thus clouded in many contexts. This volume presents participatory evaluation (PE) as a viable and creative addition to the contemporary repertoire of evaluation approaches. The authors address three basic questions: what is participatory evaluation, in what contexts is it most useful, and how does one actually do it in practice. The two primary themes in the volume are what we identify as the the principal streams in PE: practical participatory evaluation (P-PE), which is pragmatic and has as its central function the fostering of evaluation use; and transformative participatory evaluation (T-PE), which is based in emancipation and social-justice activism and focuses on the empowerment of oppressed groups. In addition to discussing these two streams, historically and philosophically, the volume examines the practical challenges of PE, by presenting it as a process of engagement and by illustrating PE through diverse case examples. Critical reflection on both practice and theory offers valuable insights into and lessons about participation and evaluation. This is the 80th issue of the quarterly journal New Directions for Evaluation.