  We survey a new generation of precision muon lifetime experiments. The goal
of the MuCap experiment is a determination of the rate for muon capture on the
free proton to 1 percent, from which the induced pseudoscalar form factor $g_P$
of the nucleon can be derived with 7 percent precision. A measurement of the
related $\mu$d capture process with similar precision would provide unique
information on the axial current in the two nucleon system, relevant for
fundamental neutrino reactions on deuterium. The MuLan experiment aims to
measure the positive muon lifetime with 20 fold improved precision compared to
present knowledge in order to determine the Fermi Coupling Constant $G_F$ to
better than 1 ppm.
