A strategy is presented in order to produce a statistically homogeneous catalog of historical and present-century earthquakes of the Aegean area by expressing the size of all these earthquakes in the moment-magnitude scale. Records of the Mainka and Wiechert intermediate period (T0 ∼ 4 sec) seismographs in Athens have been used to calculate the magnitudes of earthquakes that occurred in Greece and its surrounding area (Albania, S. Yugoslavia, S. Bulgaria, and W. Turkey) during the whole instrumental period (since 1911). This magnitude, M, has also been used to derive empirical relations with macroseismic data. It is shown here that M is equivalent to moment magnitude, MW, for a wide range of earthquake sizes (5.0 ≦ M ≦ 8.0), and to the surface-wave magnitude, MS, for large earthquake sizes (6 ≦ M ≦ 8.0). It is also shown that the local magnitude, ML, for earthquakes in Greece is half a unit smaller than the moment magnitude in the low-magnitude range (4.5 ≦ ML ≦ 6.0). This could be attributed to a magnification smaller than the nominal for the Wood-Anderson seismographs in Greece (V ∼ 1000). Relations are also proposed to calculate moment magnitude when other magnitudes (M, ML, MS, and mb) are known for earthquakes in Greece.