Monitoring and assessment of the marine and coastal environment have been central to the mandate of the MAP system since its establishment in 1975 as the first regional action plan under the UN Environment Programme’s Regional Seas Programme, and since the adoption of the Barcelona Convention one year later. For almost five decades, numerous MAP system-generated monitoring and assessment reports, including the first instalment of MED QSR issued in 2017, contributed to the accumulation of an ever-deeper body of knowledge of the marine and coastal ecosystems. The MED QSR series builds on a robust conceptual foundation and nationally sourced, quality-assured data submitted by the Contracting Parties to the Barcelona Convention or other reliable sources, to provide an evidence-based intelligible assessment of Good Environmental Status (GES) of the Mediterranean Sea and coast, based on a GES /non-GES approach, as defined in the framework of the ecosystem approach and its Integrated Monitoring and Assessment Programme IMAP.