This document discusses factors that influence whether participatory processes are effective. It presents a theory that variables like context, design, power, and scale can explain why participation works or fails. Context includes socioeconomic and cultural factors. Process design elements like involving all parties early can increase success. Power dynamics must be managed so all contributions are valued. The appropriate scale of participation depends on the spatial scale of the issues. The conclusion provides five implications for practice like understanding context, engaging early, managing power, matching engagement length to goals, and representing stakeholders at the relevant scale.