  Until recently, measurements of theta_13, which describes the nu_e component
in the nu_3 mass eigenstate, gave only upper limits, leaving open the
possibility that it is zero and eliminating a source of CP violation in the
neutrino sector. This year has seen significant advances in measuring theta_13
as precision reactor experiments move from construction phase to physics
operation and accelerator experiments give first indications that theta_13
differs from zero. In the years to come, the results from these and other
experiments will stringently test the PMNS framework for neutrino oscillation
and will start to give information about neutrino CP violation and the neutrino
mass hierarchy. This paper summarizes the situation for measuring theta_13 at
this pivotal time in neutrino research.
