This thesis describes a community psychology intervention in the Hamilton youth justice sector from September 2001 through to August 2004. I initiated the project with a Maori social service provider, Maatua Whangai, to address poor communication, gaps in service provision, and a lack of coordination and leadership in the sector. Drawing on an action research methodology the purpose of the project was to create better outcomes for youth offenders and their families by using an interagency approach to increase collaboration, coordination and the effectiveness of service delivery. My role became one of project manager and researcher. Representatives from the key agencies in the wider youth justice sector became participants and together we embarked on a journey of transformation. The group we formed, initially known as the 'Hamilton Youth Justice Collaboration', became the Hamilton Youth Offending Team (YOT), following the establishment of YOTs nationally by the Ministry of Justice in 2002. This thesis details the development of the Hamilton YOT, focusing on its purposes, methods, process, relationships and outcomes. The ten initiatives planned and implemented by the YOT are also discussed. Some of these initiatives addressed system-wide issues. Others targeted the way services were delivered by the statutory youth justice agencies. The final group of initiatives aimed to improve the knowledge of services for young people and also established services or programme to fill gaps in services. Collaborative initiatives tend to generate multiple purposes and goals aimed at multiple levels of the situation. Thus an ecological and systems approach was used to analyse the impact of the YOT's activities. This allowed for larger units of analysis at the instrumental, structural, relational and cultural dimensions of the environment. In the first instance this project created a group of agencies to provide oversight and leadership for the sector. This growth in capacity for analysing problems, devising solutions, and mobilising the required resources, allowed for the various initiatives to be implemented. YOT members spoke positively about the changes that had been made and there was a perception that the quality of service delivery had increased. The outcome evaluation that was conducted confirmed the assumption that improving communication and coordination of services, aligning service delivery with good practice, and increasing the capacity of services would equate to improved outcomes. In addition to the positive impacts on 'clients', the introduction of norms and practices that focused on cooperation and the increased opportunities for joint work, connectedness and mutual support, produced positive changes in the relational environment. While the extent to which interagency collaboration improved is considered, there is a strong focus on what was learned about the process of collaboration. The roles of the researcher and the participation by YOT members are also examined. The thesis ends with a reflection on the project as a whole, considering the major findings the study has made in the areas of action research, evaluation and collaboration.