The best reference level for use in the construction of a graph of sea-level movements in Europe during the last 15,000 years may be Normaal Amsterdam Peil (NAP) or it may be the centre of gravity of the Earth. Altitudes of dated samples of former coastal deposits now located on land or at sea must be converted to heights relative to the chosen reference level. A decision must be reached concerning what is representative of the present mean surface level of European waters. The assessment of former mean surface levels of the North Sea and the Irish Sea areas must be based almost entirely on the assessment of former mean surface levels in water bodies bordering these seas rather than on data from the sea areas themselves.