The Youth Design Assembly (YDA) is a method designed to engage young people in collaborative problem-solving and co-creation. This guide outlines its purpose, methodology, and implementation steps. It emphasizes empowering youth voices, fostering inclusivity, and generating innovative, actionable solutions to address various challenges in education, policy, and business. The guide provides a step-by-step framework, including planning, executing, and implementing assemblies, while highlighting the benefits of participation, such as deeper audience insights, improved product relevance, and sustainable community building.