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Abstract: Satellite passive-microwave radiometer-derived sea-ice concentrations have been used to investigate the spatial and temporal variability and trends of sea ice in the Laptev Sea during 24 years from 1979 through 2002. The resulting time series have been further analyzed to provide a climatology for sea-ice and polynya characteristics. The ice regime of the Laptev Sea is characterized by a large seasonal and interannual variability, the latter occurring exclusively in summer. By using a consistent sea-ice data record, we can document negative trends in all the areas studied for the 24-year period, Due to the large interannual variability the trends are not significant. For the entire Laptev Sea the decreases in sea-ice extent and area on a yearly average basis reveal −1.5% decade− 1 and −1.7% decade− 1, respectively. In summer and early fall large losses in sea-ice cover of up to 7% decade− 1 are evident in regional sectors of the Laptev Sea. In addition, an increase in polynya activity in late winter and early spring, a significant shift towards earlier snowmelt onset, and an increase of open-water area in early fall indicating an extension of the length of the summer melt period, has been observed. A brief overview of climate and sea-ice research in the Siberian Arctic is presented. According to observational data and numerical experiments there is still a large degree of uncertainty about the role of dynamic and thermodynamic factors and possible feedback mechanisms in the atmosphere–ice–ocean system, which are responsible for the large interannual variability and the retreat of sea-ice coverage as observed in the 1990s. Summer sea-ice anomalies likely result from synoptic-scale processes superimposed by the large-scale atmospheric circulation during summer and to a lesser extent from preconditioning processes in winter and spring. [Copyright &y& Elsevier]