  The Gaia mission is expected to provide highly accurate astrometric,
photometric, and spectroscopic measurements for about $10^9$ objects. Automated
classification of detected sources is a key part of the data processing. Here a
few aspects of the Gaia classification process are presented. Information from
other surveys at longer wavelengths, and from follow-up ground based
observations will be complementary to Gaia data especially at faint magnitudes,
and will offer a great opportunity to understand our Galaxy.
