Participative decision-making can offer a route toward more democratic and legitimate decisions in spatial planning processes. Although more legitimacy is sometimes presented as a result of participative decision-making, this relationship is more complex and not necessarily causal. This paper explores the relationship between the forms of legitimacy and participation by utilising the input, throughput, and output conceptualisation. In our three cases, we find that participative methods impact legitimacy differently. Participation relates to either throughput or output legitimacy depending on the objective of the participative method and process. For instance, participation allows stakeholders to voice opinions and gain insight into which stakes are balanced in spatial projects. These are typical examples of throughput legitimacy. Furthermore, in our analysis, we draw four conclusions. First, that participation often is a means to another end. For instance, it may be used to build support or attract investment in spatial projects. Second, municipalities switch between forms of legitimacy in their decision- making during participation processes. Third, timing and the long time span of projects have a major impact on participation. And finally, the municipality needs to balance multiple agendas. When this complex social, political and spatial context is not included in the equation of municipal participation, it can obstruct participation processes and delegitimise planning decisions.