In this paper we develop a conceptual framework for understanding ecologies of participation in socio-technical and democratic systems, grounded in relational co-productionist theory in STS. The framework is illustrated through empirical analysis of a systematic mapping of participation in UK energy system transitions between 2010 and 2015. This provides the first insights into system-wide patternings, diversities and inequalities of energy participation, the significant types of interrelation between practices of public engagement within wider ecologies of participation, and their mutual construction with political cultures and constitutions. The value and implications of adopting an ecologies of participation approach are considered with respect to the theoretical, empirical and practical challenges of understanding and building more inclusive, responsible and just socio-technical (energy) transitions.