Collaboration literally means working together. Collaborative improvement is an extension of continuous improvement and can be defined as a purposeful inter-company interactive process that focuses on continuous incremental innovation aimed at enhancing the collaboration’s overall performance. Developing collaborative improvement is a protracted and difficult process. Previous research has identified a number of factors affecting that process and suggested that it is not so much the individual factors, but rather their interplay that determines the successful development of collaborative improvement. This article reports research aimed at developing a deeper understanding of that interplay. Ten relationships between ten factors are presented and discussed. It appears that vision, approach, trust and commercial reality are the strongest factors. These factors are, however, influenced by, or affect the other factors, notably national culture, partner characteristics and competences, the use of power, individual behaviour and commitment. The way this interplay develops varies from case to case and has great influence on the development of collaborative improvement.