A progress report is given on our current interpretation of the X-ray emission from supernova remnants. Previous results from earlier experiments, the Einstein Observatory in particular, are reviewed and supplemented by the most recent data from the Exosat mission for a selection of remnants (Puppis-A, Cas-A, SN 1006, RCW103, W49B). Major improvements come from using the high energy spectra obtained with Exosat which indicate the presence of a very hot electron component in both young and old thermal remnants. Despite the fact that non-equilibrium ionization has been found in some cases, the spectra of most remnants investigated so far are not well represented by single non-equilibrium models, but require at least two components. An impression of the variety of plasma states which can be found in remnants is obtained from Exosat low energy filter spectroscopy of Puppis-A, which shows temperature variations on scales as small as 1′.