Previous research has increased our understanding of digital transformation (DT) and digital business ecosystems as independent topics. Less is known about how DT unfolds in digital business ecosystems. Such collaborative creation of digital innovations is affected by individual actors and by ecosystem as a whole. Based on an empirical case study of an ecosystem facilitator company and its digital business ecosystems as embedded cases, this paper contributes to the understanding of key success factors in new digital business ecosystems. The findings support collaborative governance as an important tool in leading the DT among multiple partners. Moreover, the findings present the concept of a common rulebook, including the practices, principles, guidelines, tools, handshakes, and boundaries, as an enabler for ways of working in an ecosystem. Managers can use this paper to increase their understanding on the governance of digital business ecosystems and to clarify their organisational expectations when participating in joint endeavours involving DT.