  The SNO+ experiment is located 2 km underground at SNOLAB in Sudbury, Canada.
A low background search for neutrinoless double beta ($0\nu\beta\beta$) decay
will be conducted using 780 tonnes of liquid scintillator loaded with 3.9
tonnes of natural tellurium, corresponding to 1.3 tonnes of $^{130}$Te. This
paper provides a general overview of the SNO+ experiment, including detector
design, construction of process plants, commissioning efforts, electronics
upgrades, data acquisition systems, and calibration techniques. The SNO+
collaboration is reusing the acrylic vessel, PMT array, and electronics of the
SNO detector, having made a number of experimental upgrades and essential
adaptations for use with the liquid scintillator. With low backgrounds and a
low energy threshold, the SNO+ collaboration will also pursue a rich physics
program beyond the search for $0\nu\beta\beta$ decay, including studies of geo-
and reactor antineutrinos, supernova and solar neutrinos, and exotic physics
such as the search for invisible nucleon decay. The SNO+ approach to the search
for $0\nu\beta\beta$ decay is scalable: a future phase with high
$^{130}$Te-loading is envisioned to probe an effective Majorana mass in the
inverted mass ordering region.
