Title: Precision measurements of G_F and g_P with muons.

Abstract: Two of a new generation of muon lifetime experiments will
be described.  The first, MuLAN, measures the positive muon
lifetime and provides the most precise determination of the
Fermi constant G_F, a basic parameter that sets the strength
of the weak interaction.  The second, MuCap, measures the negative
muon lifetime in ultrapure hydrogen gas.  The shorter lifetime
of the negative muon compared to that of the positive muon is
attributable to an additional disappearance mechanism, capture
on the proton.  Muon capture on the proton is sensitive to the
weak pseudoscalar form factor g_P, one of the parameters
characterizing the nucleon electroweak charged-current interaction.
There is a precise theoretical prediction for g_P based on chiral
symmetry of QCD, yet the results of past experiments are
controversial: they are dependent on a poorly-known, mu-molecular
kinetic parameter, and there is no point of mutual agreement
between theory and all experiments.  The situation was clarified
last summer with the publication of first physics results from
the MuCap experiment, which determined g_P precisely and
unambiguously.