This contains the results of X-ray analysis of the supernova remnants Cas A, RCW 86 (MSH14-63, G315.4-2.1) and SN 1006. The data comes from the ASCA, BeppoSAX and ROSAT missions. Most of the text is devoted to various aspects of the X-ray emission from Cas A, covering questions like, what is the mass of Cas A considering the high oxygen contents of the remnant?, what does the inferred mass imply for the dynamics of Cas A? what is the nature of the hard X-ray emission?, do we find evidence for the nuclear deexcitation lines associated with the decay chain of 44Ti at 68 keV and 78 keV? and what does the expansion, as observed in X-rays, tell us about the remnant? The analysis of X-ray emission from RCW 86 shows the presence of unexpected features in the X-ray spectrum. The overall line emission appears to be weak, but there is relatively strong emission of Fe-K emission at 6.4~keV associated with neutral or only weakly ionized iron. Furthermore, the morphology of the remnant changes strongly going from photon energies around 1~keV to energies above 3~keV. The change in morphology is likely to be associated with density differences in the ISM. The analysis of BeppoSAX data of SN1006 concentrates on spectral differences over the face of remnant. This includes thermal and non-thermal components (synchrotron emission). In order to do that properly care has been taken to model the effect of the point spread function of the telescopes on the spectra extracted from the different regions. This novel method uses a spatial-spectral redistribution matrix. The individual chapters of this thesis, except the introduction and conclusion and summaries (one in Dutch), have been published in A&A and Advances of Space Research.