Imprecise definition of key terms in the “public participation” domain have hindered the conduct of good research and militated against the development and implementation of effective participation practices. In this article, we define key concepts in the domain: public communication, public consultation, and public participation. These concepts are differentiated according to the nature and flow of information between exercise sponsors and participants. According to such an information flow perspective, an exercise’s effectiveness may be ascertained by the efficiency with which full, (...) relevant information is elicited from all appropriate sources, transferred to all appropriate recipients, and combined to give an aggregate/consensual response. Key variables that may theoretically affect effectiveness—and on which engagement mechanisms differ—are identified and used to develop a typology of mechanisms. The resultant typology reveals four communication, six consultation, and four participation mechanism classes. Limitations to the typology are discussed, and future research needs identified. (shrink)