This study gives an estimate of plastic accumulated in the Mediterranean Sea, an estimate of the plastic leakage flowing into the sea, and an assessment of key actions that could contribute to closing the 'plastic tap" into the sea. This study is the first of its kind to combine: (1) An estimate of the plastic stock, i.e. the quantity of plastic accumulated in the sea; (2) An estimate of the plastic leakage, i.e. the yearly flux of plastic flowing into the sea and (3) An assessment of key actions that could contribute to closing the “plastic tap” in the Mediterranean Sea.