The induced pseudoscalar coupling gp is the least well known of the weak coupling constants of the proton's charged-current interaction. Its size is dictated by chiral symmetry arguments, and its measurement represents an important test of quantum chromodynamics at low energies. During the past decade a large body of new data relevant to the coupling gp has been accumulated. This data includes measurements of radiative and non radiative muon capture on targets ranging from hydrogen and few-nucleon systems to complex nuclei. Herein the authors review the theoretical underpinnings of gp, the experimental studies of gp, and the procedures and uncertainties in extracting the coupling from data. Current puzzles are highlighted and future opportunities are discussed.