Metal-ceramic systems play very important role in the prosthetic dentistry. The most widely used metallic alloys are the Ni-Cr, Co-Cr, Au-based alloys and Ti. The bonding strength between the metal base and the ceramic covering layer can be very different in different systems and is strongly affected by the firing conditions as well. For the further improvement of the bonding properties the detailed knowledge of the microstructure of the metal-ceramic interlayer is essential. In this work our results, obtained by scanning and transmission electron microscopy on systems of commercial alloys and corresponding porcelains will be reviewed.