This Knowledge Brief produced by NetworkNature aims to disentangle the complexities associated with the integration of research and policy with regards to nature-based solutions (NBS) implementation and mainstreaming. The brief provides an overview of the NBS knowledge gaps resulting from an analysis by NetworkNature of a large number of research publications, an online consultation and strategic dialogues with key stakeholders. This can support policymakers in better understanding the research needs which can strengthen the implementation of NBS. In preparation of this knowledge brief, interviews with policy makers and policy think tanks have been a major contributing source. The interviews reinforced key barriers to policy implementation for NBS and created better insight in priorities for research on NBS. The knowledge brief concludes with a list of recommendation for policymakers to address the identified gaps and barriers.