  The CERN LHC delivered 25/fb of proton-proton collision data in 2011-2012 at
sqrt{s} = 7 - 8 TeV centre-of-mass energy to the ATLAS detector. These Run 1
data were used to discover the Higgs boson and measure its properties as well
as to perform numerous other tests of the Standard Model via precision
measurements and searches for New Physics. In preparation for the Run 2 data
taking at sqrt{s} = 13 TeV, the collaboration embarked on an upgrade program
during the long LHC machine shutdown in 2013-2015. The early 2015 data set was
then used to promptly recommission the apparatus allowing the first physics
results to appear already in the summer of 2015. After briefly reviewing the
upgrade and the improved performance of the detector, this paper concentrates
on the final Run~1 results on Higgs, W and Z boson, electroweak multi-boson and
top quark production as well as on searches for supersymmetry and other new
phenomena.
