  Gaia Data Release 3 contains a wealth of new data products for the community.
Astrophysical parameters are a major component of this release. They were
produced by the Astrophysical parameters inference system (Apsis) within the
Gaia Data Processing and Analysis Consortium. The aim of this paper is to
describe the overall content of the astrophysical parameters in Gaia Data
Release 3 and how they were produced. In Apsis we use the mean BP/RP and mean
RVS spectra along with astrometry and photometry, and we derive the following
parameters: source classification and probabilities for 1.6 billion objects,
interstellar medium characterisation and distances for up to 470 million
sources, including a 2D total Galactic extinction map, 6 million redshifts of
quasar candidates and 1.4 million redshifts of galaxy candidates, along with an
analysis of 50 million outlier sources through an unsupervised classification.
The astrophysical parameters also include many stellar spectroscopic and
evolutionary parameters for up to 470 million sources. These comprise Teff,
logg, and m_h (470 million using BP/RP, 6 million using RVS), radius (470
million), mass (140 million), age (120 million), chemical abundances (up to 5
million), diffuse interstellar band analysis (0.5 million), activity indices (2
million), H-alpha equivalent widths (200 million), and further classification
of spectral types (220 million) and emission-line stars (50 thousand). This
catalogue is the most extensive homogeneous database of astrophysical
parameters to date, and it is based uniquely on Gaia data.
