Brief outline of the overall workshop: Global public health challenges such as climate change, non-communicable diseases, and health inequalities are driven by innumerable interacting factors. Tackling these challenges is increasingly recognised as requiring new and large teams from a wide range of disciplines and sectors spanning large and complex systems, who must identify and agree the root causes of problems to target. The challenge of problem identification becomes substantially greater in complex systems, and for large teams with heterogenous backgrounds, expectations, and priorities. This workshop looks at how large research teams can identify and develop shared understandings of problem areas in complex systems, with a view to fostering effective collaboration with critical, targeted stakeholders. Through presentations introducing key concepts followed by structured small group work and whole group debate, participants will hear and contribute to Discussions on problem identification within large research teams and approaches to targeted stakeholder engagement in complex systems. The workshop draws on the presenters' critical reflections from TRUUD (Tackling the Root Cause Upstream of Unhealthy Urban Development), a five-year collaboration between five universities in the United Kingdom and their partners in industry, government, and the public. Specific Aims/ Objectives and Component Parts: This workshop aims to develop knowledge and ideas that can support large teams to develop shared conceptualisations of complex public health problems. Key objectives are i) to share knowledge about the challenges of problem identification in large research teams and understand why this is critical for tackling complex public health challenges, ii) to define what constitutes good co-production of problem identification with stakeholders in a complex system, and iii) to improve knowledge of the processes and tools that can support large teams to develop shared understandings on these issues. The workshop will include a mixture of presentations, audience questions, and structured discussions in small groups. Firstly, facilitators will share their learnings from the TRUUD project on problem identification and developing shared understandings in inter- or trans-disciplinary teams, and stakeholder engagement in complex systems. Secondly, workshop attendees will be invited to ask questions to the facilitators and to share their reflections on key concepts. Thirdly, attendees will be divided into small groups to debate issues in engaging the wide range of stakeholders relevant to research on complex public health problems, including how to identify stakeholders and when engagement should occur. The session will conclude with a final plenary session where groups will feed back their ideas and we will identify areas of consensus for approaches to stakeholder engagement in a complex system. Key questions that the workshop will seek to address: The workshop will explore the overall question 'How can large research teams conceptualise and develop shared understandings of complex health problems to support intervention development?'. Sub-questions include: 1. How can researchers from multiple disciplines develop shared understandings of complex problem spaces? 2. How can stakeholder engagement be managed to help identify and understand problem spaces in complex systems? 3. What tools, methods, and processes help teams to coalesce around specific problems in complex systems?