  The third Gaia data release contains, beyond the astrometry and photometry,
dispersed light for hundreds of millions of sources from the Gaia prism spectra
(BP and RP) and the spectrograph (RVS). This data release opens a new window on
the chemo-dynamical properties of stars in our Galaxy, essential knowledge for
understanding the structure, formation, and evolution of the Milky Way. To
provide insight into the physical properties of Milky Way stars, we used these
data to produce a uniformly-derived, all-sky catalog of stellar astrophysical
parameters (APs): Teff, logg, [M/H], [$\alpha$/Fe], activity index, emission
lines, rotation, 13 chemical abundance estimates, radius, age, mass, bolometric
luminosity, distance, and dust extinction. We developed the Apsis pipeline to
infer APs of Gaia objects by analyzing their astrometry, photometry, BP/RP, and
RVS spectra. We validate our results against other literature works, including
benchmark stars, interferometry, and asteroseismology. Here we assessed the
stellar analysis performance from Apsis statistically. We describe the
quantities we obtained, including our results' underlying assumptions and
limitations. We provide guidance and identify regimes in which our parameters
should and should not be used. Despite some limitations, this is the most
extensive catalog of uniformly-inferred stellar parameters to date. 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 (5 million), diffuse interstellar band analysis (1/2 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). More precise and detailed astrophysical parameters based on
epoch BP, RP, and RVS are planned for the next Gaia data release.
