Children and teens placed in out-of-home care experience a long-term disadvantage in virtually all health-related and socioeconomic outcomes compared to youth who do not have this experience. Few interventions that aim to support youth in leaving out-of-home care and help them prepare for adult life have been identified in the scientific literature. Even fewer have evidence of being effective. As a response to the lack of consistent support for young care leavers in Sweden, two attempts to develop transition services have been initiated during the past few years. Practice experience of intervention development has not been leveraged in scientific research and though many theoretical frameworks for intervention development have emerged in recent years, such frameworks are often developed by researchers, for researchers. Still, most interventions are developed by practitioners, in local, practice settings. Research indicates that locally developed interventions seem to be more successful than interventions that are adopted without adaptation. Investigating how practitioners approach conceptualization and development of interventions can provide an important insight into how interventions can better be designed to fit the needs of those for whom they are designed and increase our theoretical and empirical understanding of this process. By exploring the development process of locally developed interventions for youth leaving out-of-home care in Sweden, the aim of this project is to contribute to the intervention development literature by investigating the possibility for researchers to learn from practice about how we can develop more effective and ethical interventions for vulnerable populations. Interviews with developers of preventive interventions for youth will explore activities and priorities in the practice-based intervention development processes and how these compare and contrast across a spectrum of approaches to intervention development in the scientific literature. Preliminary results and implications for future practice and research will be discussed based on the interviews.