NWO has requested CWTS to analyze the extent to which research funded by NWO is made openly accessible. In 2009, NWO introduced its first open access (OA) policy, stating that publications funded by NWO should be made openly accessible ‘as soon as possible’. Following the Dutch OA ambitions presented by state secretary Sander Dekker in 2013, NWO turned its OA policy into a formal mandate in 2015. According to this mandate, all publications funded by NWO must be openly accessible at the time of publication, preferably through the gold OA route, although the green OA route is also supported. This mandate should make sure that NWO funded research meets the OA targets set by the Dutch government. According to these targets, of all publicly funded publications, 60% should be openly accessible in 2018 and 100% in 2020. To monitor NWO’s progress in making the publications it funds openly accessible, this report presents statistics on the extent to which publications from the period 2015–2018 funded by NWO are openly accessible. Separate statistics are presented for publications funded by ZonMW and for publications of the national research institutes managed by NWO. Throughout the report, a distinction is made between gold, hybrid, bronze, and green OA. The report also discusses differences in citation impact between OA and non-OA publications.