  The Daya Bay experiment was the first to report simultaneous measurements of
reactor antineutrinos at multiple baselines leading to the discovery of
$\bar{\nu}_e$ oscillations over km-baselines. Subsequent data has provided the
world's most precise measurement of $\rm{sin}^22\theta_{13}$ and the effective
mass splitting $\Delta m_{ee}^2$. The experiment is located in Daya Bay, China
where the cluster of six nuclear reactors is among the world's most prolific
sources of electron antineutrinos. Multiple antineutrino detectors are deployed
in three underground water pools at different distances from the reactor cores
to search for deviations in the antineutrino rate and energy spectrum due to
neutrino mixing. Instrumented with photomultiplier tubes (PMTs), the water
pools serve as shielding against natural radioactivity from the surrounding
rock and provide efficient muon tagging. Arrays of resistive plate chambers
over the top of each pool provide additional muon detection. The antineutrino
detectors were specifically designed for measurements of the antineutrino flux
with minimal systematic uncertainty. Relative detector efficiencies between the
near and far detectors are known to better than 0.2%. With the unblinding of
the final two detectors' baselines and target masses, a complete description
and comparison of the eight antineutrino detectors can now be presented. This
paper describes the Daya Bay detector systems, consisting of eight antineutrino
detectors in three instrumented water pools in three underground halls, and
their operation through the first year of eight detector data-taking.
