  The main physics goal of the SNO+ experiment is the search for neutrinoless
double-beta decay (0$\nu\beta\beta$), a rare process which if detected, will
prove the Majorana nature of neutrinos and provide information on the absolute
scale of the neutrino mass. Additional physics goals include the study of solar
neutrinos, anti-neutrinos from nuclear reactors and the Earth's natural
radioactivity as well as Supernovae neutrinos. Located in the SNOLAB (Canada)
deep underground laboratory, it will re-use the SNO detector. A short phase
with the detector completely filled with water has started at the beginning of
2017, before running the detector with scintillator. This paper describes in
details the SNO+ sensitivity to 0$\nu\beta\beta$ decays, as well as the other
physics goals. Crucial to these large volume liquid scintillator experiments,
is the ability to constraint the low-energy background from radioactive decays.
Methods to mitigate those are also presented.
