Open Process Innovation provides a framework for studying how to systematically make use of knowledge that lies outside of an organization’s boundaries for process innovation initiatives. Here, we seek to investigate into variables that impact on the qualities of Open Process Innovation taking the example of the public sector domain. This paper examines how a lack of resources impacts on BPM. Specifically in investigates how personnel resource scarcity exerts influence on the involvement of i) customers (here citizens and local companies) and ii) consultants (here management and software consultants) in public sector BPM. Our multi-method analysis shows that personnel resource scarcity has consequences for BPM-related collaboration schema as it restricts the involvement of customers. Based on our findings, implications for theory and practice are discussed, including implications for studies on BPM maturity or on business process design. We call for a governancetheory perspective on process innovation as a fundamental basis for understanding and designing the institutions that shape collaboration in open process innovation.