With the coordination of health care services becoming increasingly complex, the challenges of fragmentation cannot be solved by administrative restructuring alone. Attention must also be given to the coordination practices of professional groups, and, in this respect, the nursing profession is a particularly interesting case. Based on a qualitative case study of Danish nurses in hospital, municipality, and general practice, this article addresses the following question: How does the nursing profession practice formal and informal inter-organisational coordination in complex pathways, and what is the interplay between the 2 types of coordination? The findings contribute to our knowledge of coordination at the operative level of health care by identifying specific informal practices in inter-organisational coordination and by showing how informal coordination is activated to support formal coordination in a concurrent organisational and professional ambition of integration. The nurses studied here proved very loyal to formal inter-organisational coordination mechanisms, prioritising them as first choices of action. When formal procedures were found insufficient, however, the nurses temporarily switched to informal coordination. This was triggered by random encounters with fragmentation, a strong professional engagement in making things work in the interest of the patient, and a constant striving to be on top of things. Informal inter-organisational coordination is broken down into supplementary and by-passing practices, and 4 specific by-passing practices are identified. The discussion offers insight into how a lack of agency related to formal inter-organisational coordination can be related to negotiated settlements, and informal coordination is considered in terms of "rule bending" within complex systems.