Public decisions unfold in environments defined by complexity and interdependence, making effective stakeholder engagement essential for sound governance. Engagement links institutions with the people and organisations affected by their choices, ensuring that initiatives, from policy development to the use of Local Digital Twins, are grounded in real contexts and informed by diverse forms of knowledge. Design provides a structured way to approach this work. It encourages institutions to understand the systems in which decisions occur, clarify who should be involved, and align methods with the purpose of each phase. The co-creation model (lab, studio, arena, agora) helps distinguish different collaboration settings and the roles stakeholders play within them, supporting more deliberate, meaningful, and adaptive engagement. This learning unit introduces key principles and methods for stakeholder engagement in public decision-making. Learners explore how to design stakeholder discovery and selection, how to balance social and technical dimensions in digital environments, and how structured engagement strengthens transparency, learning, and the legitimacy of public decisions.