  Borexino is a large-volume liquid scintillator detector installed in the
underground halls of the Laboratori Nazionali del Gran Sasso in Italy. After
several years of construction, data taking started in May 2007. The Borexino
phase I ended after about three years of data taking. Borexino provided the
first real time measurement of the $^{7}$Be solar neutrino interaction rate
with accuracy better than 5% and confirmed the absence of its day-night
asymmetry with 1.4% precision. This latter Borexino results alone rejects the
LOW region of solar neutrino oscillation parameters at more than 8.5 $\sigma$
C.L. Combined with the other solar neutrino data, Borexino measurements isolate
the MSW-LMA solution of neutrino oscillations without assuming CPT invariance
in the neutrino sector. Borexino has also directly observed solar neutrinos in
the 1.0-1.5 MeV energy range, leading to the first direct evidence of the $pep$
solar neutrino signal and the strongest constraint of the CNO solar neutrino
flux up to date. Borexino provided the measurement of the solar $^{8}$B
neutrino rate with 3 MeV energy threshold.
