Within CONNECTING Nature, we are dealing with developing innovative nature-based solutions (NBS) for climate change adaptation, health and well-being, social cohesion and sustainable economic development in European cities. In order to enable "learning by comparing" and "generating new knowledge" from multiple NBS related studies, a novel data and knowledge base is needed which requires a specified methodological approach for its development. This paper provides conceptual and methodological context and techniques for constructing such a data and knowledge base that will systematically support the process of NBS monitoring and assessment:•A methodology presents the comprehensive, multi-step approach to the NBS data and knowledge development that helps to guide work and influence the quality of an information included.•The paper describes the methodology and main steps/phases for developing a large data and knowledge base of NBS that will allow further systematic review.•The suggested methodology explains how to build NBS related databases from the conceptualization and requirements phases through to implementation and maintenance. In this regard, such a methodology is iterative, with extensive NBS stakeholders' and end-user's involvement that are packaged with reusable templates or deliverables offering a good opportunity for success when used by practitioners and other end-users.•The NBS data and knowledge base gathers information about different NBS models and generations into one easy-to-find, easy-to-use place and provides detailed descriptions of each of the 1490 NBS cases from urban centers in Europe.•The data and knowledge base thus helps users identify the best and most appropriated NBS model/type for addressing the particular goals and, at the same time, considers the local context and potential.•The data obtained can be used for the further meta-analysis by applying statistics or searching for specific sample cases and thus enables to generate and expand the knowledge from multiple NBS related studies, in both qualitative and quantitative ways.