  The U(1)' symmetry associated with a possible heavy Z' would have profound
implications for particle physics and cosmology. The motivations for such
particles in various extensions of the standard model, possible ranges for
their masses and couplings, and classes of anomaly-free models are discussed.
Present limits from electroweak and collider experiments are briefly surveyed,
as are prospects for discovery and diagnostic study at future colliders.
Implications of a Z' are discussed, including an extended Higgs sector,
extended neutralino sector, and solution to the mu problem in supersymmetry;
exotic fermions needed for anomaly cancellation; possible flavor changing
neutral current effects; neutrino mass; possible Z' mediation of supersymmetry
breaking; and cosmological implications for cold dark matter and electroweak
baryogenesis.
