Electron impact ionization and dissociation studies of C60and C70carried out in our laboratory over the past three years have revealed many exciting and novel features of this new class of molecules (clusters). The most salient results are summarized in this paper, including first a description of the crossed beams apparatus and the various mass spectrometric (two-sector field) techniques used. This is followed by a discussion of the production of parent and fragment ions (with up to eight charges) via electron impact ionization of C60and C70including results on mass spectral fragmentation patterns and measured and calculated absolute ionization cross-section functions. The experimental results concerning the energetics of produced parent and fragment ions are presented in the next section and measured appearance energies and breakdown curves are analysed in the frame of various theoretical concepts (Rrkm, Fhbt) thereby allowing us to derive the corresponding binding energies. The last section is devoted to (i) the different aspects of the stability of singly- and multiply-charged fullerene ions (i.e. the quantitative study of various unimolecular decay channels such as monomer evaporation, sequential decay series, charge separation reactions, etc.) and, based on the measured properties of these decay reactions, to (ii) a discussion of the possible decay mechanisms.