In austral winter large regions of the Southern Ocean are covered by seasonal sea ice which disappears in summer. Only in few regions sea ice persists during the summer and becomes second-year ice. Most of this second-year ice is located in the Weddell Sea, making this region particularly interesting. The variation of the ice-covered area modifies the exchange of heat, mass and momentum between ocean and atmosphere. Therefore knowledge of ice extent and its variability is necessary for an adequate simulation of those fluxes and thus for climate modelling. The goal of this study is the observation of interannual and seasonal ice-extent variations and their underlying causes in the Weddell Sea. Variability is analysed by using microwave satellite data. Results are correlated with satellite-derived sea-ice drift data and with ice-drift fields calculated from a Finite Element Sea ice–Ocean Model (FESOM) to determine the impact of ice-drift variations on sea-ice extent. An additional cause for variations of ice extent could be different ice type distributions, i.e. the contribution of first- and second-year ice to the total ice-covered area. These ice types are determined on monthly timescales from scatterometer satellite data for the years 2000–2007 and will be extended backward in time using the ice-thickness distribution modelled by FESOM. Ice-class distribution and sea-ice drift variability are compared with the characteristics and variability of meteorological behaviour to evaluate the relative importance of different sea-ice parameters for shaping Weddell Sea ice extent and its variability.