The chapter introduces the One Health implementation cycle with all steps that occur during the implementation of a project or policy. We start with an introduction to the implementation of activities in socio-ecological systems (SES), which are, by definition, complex and dynamic. We then explore the kind of challenges we encounter in SES and how these determine the importance of engaging stakeholders in the problem statement, in the understanding of the SES itself and in the co-production of solutions. The cycle starts with stating the problem in an inclusive way and exploring the stakeholders systematically, to leave no one behind. Then, we start a community of practice by co-producing a common understanding of the SES and the challenge. We then reach out and will discover what conflicting perspectives and interests we may encounter and how to deal with them to align behind a common theory of change. This forms the basis for other parts in the implementation cycle, which are covered in Chapters 11, 12 and 13.