  The European Space Agency's Planck satellite, dedicated to studying the early
Universe and its subsequent evolution, was launched 14~May 2009 and scanned the
microwave and submillimetre sky continuously between 12~August 2009 and
23~October 2013. In February~2015, ESA and the Planck Collaboration released
the second set of cosmology products based on data from the entire Planck
mission, including both temperature and polarization, along with a set of
scientific and technical papers and a web-based explanatory supplement. This
paper gives an overview of the main characteristics of the data and the data
products in the release, as well as the associated cosmological and
astrophysical science results and papers. The science products include maps of
the cosmic microwave background (CMB), the thermal Sunyaev-Zeldovich effect,
and diffuse foregrounds in temperature and polarization, catalogues of compact
Galactic and extragalactic sources (including separate catalogues of
Sunyaev-Zeldovich clusters and Galactic cold clumps), and extensive simulations
of signals and noise used in assessing the performance of the analysis methods
and assessment of uncertainties. The likelihood code used to assess
cosmological models against the Planck data are described, as well as a CMB
lensing likelihood. Scientific results include cosmological parameters deriving
from CMB power spectra, gravitational lensing, and cluster counts, as well as
constraints on inflation, non-Gaussianity, primordial magnetic fields, dark
energy, and modified gravity.
