ESA’s cornerstone Gaia mission will acquire observations of a billion stars and other objects of the Milky Way, resulting in the construction of a three-dimensional stellar map of our galaxy. However, Gaia’s "eyes" will be able to see further away, observing millions of Local Group stars, distant galaxies and quasars. Gaia will record the spectra of the detected extragalactic objects, but the morphological information could also be retrieved, too. Extragalactic astronomy will be highly benefited from the huge database that the Gaia satellite will obtain through its five years of operations. The proper exploitation of these data is therefore of a great importance of the astronomical community.
The galaxy spectra of the distant unresolved galaxies and the stellar spectra of the Local Group resolved galaxies will be used to predict, among others, spectral classes, redshift and extinction values and star formation history parameters, and to define key properties of star forming regions, improving our understanding of the star formation history, distance and age scales and evolution of the Universe.
The urgent pre-mission needs of Gaia and the proper future exploitation of extragalactic Gaia data require the complementary use of other space and ground-based surveys. Discovering the scientific information from these huge databases requires the implementation of advanced classification and parameterization software and galaxy evolution codes, with the aid of realistic synthetic data. Astrostatistics and synthetic galaxy templates will facilitate the exploitation of Gaia data and maximize their impact.