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This paper reviews both the current and previous studies of the Baltic Yoldia stage along with their alternative interpretations of the results and events. Focus is placed on the Tallinn area in northern Estonia. On the basis of palaeogeographical and diatom-stratigraphical studies, the changes in the palaeoenvironment, during the transition from late glacial to early Holocene (Preboreal) conditions, are described. The Tondi and Sojamae mires at altitudes just around the Yoldia level of the area (ca. 40 m a.s.l.) show only very slight influence of the brackish Yoldia Sea in their supralittoral to littoral environment. The two sites at lower altitudes with a Yoldia water-depth of approx. 40 m at Pirita and approx. 60 m at Harku, register pronounced brackish water conditions in their diatom assemblages, characteristic of the littoral to sublittoral environment of the Yoldia Sea. The litho- and biostratigraphical data cannot confirm a transgressive nature of the Baltic during the brackish Yoldia stage, but are rather suggesting a regressive development of shoreline. According to the present study the diatom composition of the Yoldia sediments was dependent on the depositional environment, and the abundance of saline water diatoms increased with water depth. The influx of older, redeposited, marine diatoms was here of minor importance.