The European Directive 2001/77/EC on the promotion of electricity produced from renewable energy sources, in the internal electricity market, imposes a target figure for the contribution of the production of electricity from renewable energy sources upon each Member State. For Belgium, this target figure is 13% of the total energy consumption, which must be achieved by 2020. Offshore wind farms in the Belgian part of the North Sea are expected to make an important contribution (ca. 43%, assuming 2000 MW installed capacity by 2020) to achieve that goal. Within the Belgian part of the North Sea (BPNS), a zone of 238 km² is reserved for the production of electricity from water, currents or wind. Four wind farms are already operational. With five more to come, major ecological changes may however be expected. Prior to installing a wind farm, a developer must obtain a domain concession and an environmental permit. The environmental permit includes a number of terms and conditions intended to minimise and/or mitigate the impact of the project on the marine ecosystem. Furthermore, as required by law, the permit imposes a monitoring programme to assess the effects of the project onto the marine environment. Within the monitoring programme, the Royal Belgian Institute of Natural Sciences and its partners assess the extent of the anticipated impacts on the marine ecosystem and aim at revealing the processes behind these impacts. The first objective is basically tackled through the baseline monitoring, focusing on the a posteriori, resultant impact quantification, while the second monitoring objective is covered by targeted or process monitoring, focusing on cause-effect relationships of a priori selected impacts. As such, baseline monitoring deals with observing rather than understanding impacts and hence leads to area-specific results, which might form a basis for halting activities. This report, targeting marine scientists, marine managers, policy makers and offshore wind farm developers, presents an overview of the scientific findings of the Belgian offshore wind farm monitoring programme, based on data collected unto 2016.