This paper introduces a classification of coastal dune system into two main morphodynamic classes, namely retentive and transgressive dune systems. Retentive system include coastal dune types where sand accumulation within vegetation is dominant over other processes. In the category we include such morphological types as hummock dunes, foredunes, and retention ridges, including sub-environments such as preciptation ridges that form the landward boundary of transgressive dunefields. Transgressive system include those coastal dune types where sand transport is dominant over other processes, and the dunes are unvegetated and mobile. In this cateory we include such morphological types as parabolic dunes, reversing transverse dunes, barchans, seif dunes, transgressive sheet dunefields and headland-bypass dunefields.