Gaia Data Release 3 contains a wealth of new data products for the community. Astrophysical parameters are a major component of this release,and were produced by the Astrophysical parameters inference system (Apsis) within the Gaia Data Processing and Analysis Consortium (DPAC).The aim of this paper is to describe the overall content of the astrophysical parameters in Gaia DR3 and how they were produced. In Apsis, we usethe mean BP/RP and mean RVS spectra along with astrometry and photometry, and we derive the following parameters: source classification andprobabilities for 1.6 billion objects; interstellar medium characterisation and distances for up to 470 million sources, including a 2D total Galacticextinction map; 6 million redshifts of quasar candidates; 1.4 million redshifts of galaxy candidates; and an analysis of 50 million outlier sourcesthrough an unsupervised classification. The astrophysical parameters also include many stellar spectroscopic and evolutionary parameters for upto 470 million sources. These comprise Teff , log g, and [M/H] (470 million using BP/RP, 6 million using RVS), radius (470 million), mass (140million), age (120 million), chemical abundances (up to 5 million), diffuse interstellar band analysis (0.5 million), activity indices (2 million), Hαequivalent widths (200 million), and further classification of spectral types (220 million) and emission-line stars (50 000). This paper is the firstin a series of three papers, and focusses on describing the global content of the parameters in Gaia DR3. The accompanying papers II and IIIfocus on the validation and use of the stellar and non-stellar products, respectively. This catalogue is the most extensive homogeneous database ofastrophysical parameters to date, and is based uniquely on Gaia data. It will only be superseded by Gaia Data Release 4, and will therefore remaina key reference over the next four years, providing astrophysical parameters independent of other ground- and space-based data.< Leer menos