The CO-CREATE project focuses on the need for research on obesity prevention in adolescents to move away from studies of single interventions, toward the investigation of systems-based research incorporating youth involvement. This paper provides an overview of the project, presenting the objectives, design, and novel methodologies applied, as well as findings to date and anticipated outcomes. Adolescents (16-18 years old) in five European countries participated. Methods applied in the project include monitoring and benchmarking of policies, systematic literature reviews, epidemiological surveillance, linking observed overweight and obesity trends to observed policy landscapes, group model building to identify perceived drivers of obesity, alliance building with adolescents, dialog with stakeholders, and system dynamics modelling to explore the potential impact of policy options. Outcomes include tools for developing policy ideas and investigation of prevention strategies with adolescents, including policy databases, system maps of drivers of obesity, protocols for organizing youth alliances, an intergenerational policy dialog tool, and system dynamic models exploring the impacts of cocreated policy ideas. These outcomes make an important contribution to building a pan-European infrastructure for designing and evaluating policies and for providing youth with the opportunity to make their voices heard in the development and implementation of obesity prevention measures.