The nucleon axial radius, its determination and implications

The nucleon axial radius, $r_A^2$, is an important quantity governing the nucleon response to electroweak probes. Its uncertainty dominates the error bar for neutrino-nucleon charged current quasielastic scattering, a key signal process at long baseline neutrino experiments. Recent developments are reviewed, including the reanalysis of data from neutrino scattering at deuterium bubble chambers and the reinterpretation of muon capture on hydrogen as a measurement of $r_A^2$; these processes currently provide the best constraints on $r_A^2$. The talk concludes with an overview of current and future theoretical and experimental efforts for improved measurements of $r_A^2$.