Cities around the globe face important challenges to adapt to climate change, but while nature-based solutions (NBS) are considered as a promising strategy to do so, we do not yet have a good understanding of how NBS are conceptualized and implemented by city governments in practice. The overarching assumption, based on an extensive literature review, states that effective implementation of NBS requires urban partnerships. However, very little is known about what these partnerships for NBS look like (gap 1), how they function (= gap 2), and with what results (= gap 3). This project aims to fill these knowledge gaps by focusing on the following research question: "How do cities in the European Union understand and implement nature-based solutions in partnerships, why, and with what effects?". This question is dealt with using a QCA-research design, to allow cross-country analysis via in-depth case studies of cities in the European Union. This analysis will draw on documents (i.e. climate adaptation strategies and plans) and semi-structured elite interviews with politicians, administrators, and non-public actors in the cities’ partnerships. This will lead to a framework for both academics and practitioners to analyze NBS and partnerships in urban contexts, taking account of the different determinants contributing to different types of partnerships, their functioning, and their impact.