Diatom and radiocarbon data of two cores from the north-eastern part of the western Belgian coastal plain are discussed. The palaeoenvironmental reconstruction of these sites and additional stratigraphic and geochronological information, allow an assessment of the general development of this region throughout the Holocene. Prior to c. 7500 yrs cal. BP a rapidly transgressing coast exists. Basal peat development may have been fairly wide­spread. Extensive erosion channels form towards the interior once the volume of the developing tidal basin has in­creased sufficiently. In spite of very high rates of sediment accumulation, high-intertidal environments remain poorly developed due to the high rate of RSL rise and the relatively steep slope of the transgressed terrain. Diatom taphocoenoses of this period consist primarily of coastal tychoplankton (mainly Cymatosira belgica), deposited in association with flood transported sediment, and some epipsammon. Hereafter, the incidence of negative tendencies in marine influence increases, culminating between c. 6300 to 5600 yrs cal. BP. Diatom assemblages are now more varied with an improved representation of tidal flat and salt marsh communities. The marine species Paralia sulcata and Pseudopodosira westii become abundant in high intertidal deposits, which may involve selective transport, sedi­mentation and preservation mechanisms. In general, the environmental changes reflect the development of a broad intertidal sedimentation zone in which sediment supply remained high, combined with a gradual slowing down of the RSL rise. Coastal progradation finally leads to sufficiently sheltered conditions for long-lasting peat growth in the intracoastal area up to perhaps c. 2100 yrs cal. BP Presumably a coastal barrier, which remains intersected by some inlets, also develops during this period. At places, peat growth is interrupted at about 4200 yrs cal. BP by a marked but short-lived period of marine sedimentation. Within the general framework of a return to a transgressive ...