This chapter proposes a set of robust evaluative criteria for public participation processes, grounded in deliberative democratic theory and informed by extensive scholarship on best practices. A wide range of frameworks is examined, from Arnstein’s seminal “ladder of citizen participation” to the Organization for Economic Co-operation and Development (OECD)’s contemporary guidelines, culminating in a synthesized taxonomy centered on input, process, and outcome legitimacy. This approach highlights the essential roles of inclusiveness, clarity of purpose, agency commitment, procedural fairness, knowledge validation, and constructive deliberation in shaping meaningful engagements. In parallel, the chapter emphasizes how well-designed participatory processes foster public trust, address complex policy problems effectively, and build lasting capacity among citizens, stakeholders, and officials. By grouping criteria into three temporal phases—preparation, conduct, and results—the chapter provides a guiding structure for evaluating diverse formats of participation, from routine regulatory consultations to collaborative problem-solving for contentious environmental decisions. Throughout, real-world examples illustrate how to operationalize these benchmarks. The result is a flexible yet rigorous tool that scholars and practitioners alike can use to design, implement, and assess more legitimate, equitable, and impactful public engagement initiatives.