  Beta-decay and muon-capture experiments in nuclei are reviewed. The conserved
vector current hypothesis is confirmed through the observed constancy of the
vector coupling constant determined from the superallowed Fermi transitions and
from the measurement of the weak-magnetism term in mirror Gamow-Teller
transitions. The axial-vector and pseudoscalar coupling constants in the
nucleon are determined from neutron decay and muon capture on the proton
respectively. In finite nuclei, evidence for these coupling constants being
reduced relative to their free-nucleon values is discussed. Meson-exchange
currents are shown to be an important correction to the time-like part of the
axial current as evident in first-forbidden beta decays. Tests of the Standard
Model are discussed, as well as extensions beyond it involving right-hand
currents and scalar interactions.
