Health-care systems currently face great challenges, including an increasing elderly population. To respond to this problem, a hospital emergency department, three municipalities, and self-employed general practitioners in Denmark decided to collaborate with the aim of reorganizing treatment of elderly acute ill patients. By establishing a small-scale collaborative community and through an action research process, we show, how to jointly explore and develop a new organization design for in-home hospital treatment that enables the health professionals to collaborate in new ways, and at the same time to investigate and improve this cocreation process and codesign of knowledge among multiple different stakeholders.