In the domain of climate change adaptation, joint knowledge production (JKP) through intensive cooperation between scientists, policy-makers, and other actors is often proposed as a means to reconcile supply and demand for knowledge. Regional adaptation projects in the Netherlands form prominent examples of this. However, there is a lack of systematic empirical studies on how JKP can be done successfully. Here, we take the next step toward generating design principles for JKP. We do so by carrying out a comparative analysis of six Dutch adaptation projects using a previously developed assessment framework. Project documents were studied, and 30 semi-structured interviews were held with researchers, policy-makers, and financiers in the projects. Based on project comparisons, we derive and elaborate on two design principles for JKP. First, the most successful projects managed to create what we term a protected space for knowledge development while establishing connections with ongoing policy processes. Successful JKP seems to be more likely in cases in which actors make a conscious decision for the institutional location of the project on the research–policy nexus, whereby the coordinating entity has some characteristics of a boundary organization. Second, specific resources, including facilities, boundary objects, and specific competencies increase the chance for success.