OBJECTIVE: This qualitative study explores the experiences of stakeholders in implementing the guidance for early-intervention services (EIS) for first-episode psychosis in England. One important challenge in implementing early-intervention policy is to develop workable, integrated partnership across a number of diverse organizational boundaries, particularly with child and adolescent mental health services (CAMHS). METHODS: A series of 142 semistructured interviews and six focus groups involving 31 people were undertaken between February 2004 and September 2007. A broad range of individuals were interviewed from different strategic, managerial, and operational levels of the health service. RESULTS: A main finding was the challenge experienced by a majority of EIS agencies in developing partnerships with CAMHS. Elements that led to more successful partnership development included joint learning and training, senior-level "champions" of the partnership, joint operational policy or protocol development, and use of specific CAMHS-EIS link workers. The most successful approach was to develop a separate youth-focused service that placed multiple teams and organizations responsive to younger people's needs (including education, employment guidance, social activities, pregnancy services, and peer support) under one roof. CONCLUSIONS: This study highlights that traditional hierarchical models of policy implementation may be less successful in achieving the goal of collaborative partnerships at the interface between CAMHS and EIS. The most successful model of working between CAMHS and EIS required an innovative approach to commissioning, policy implementation, and service development. The findings from this study may help determine the best model of partnership development for EIS and CAMHS in England.