Pion interferometry: Recent results from SPS

Recent results from the CERES experiment at the SPS are reviewed. Emphasis is put on the centrality and beam energy dependence, and the results are put into perspective with findings at lower and higher beam energies. The rather weak beam energy dependence of the HBT radii maybe understood in terms of a transition from baryon to pion dominated freeze-out. The observed short lifetimes end emission durations are presently in contradiction to results from model calculations.