  Future muon colliders will have remarkable capability for revealing and
studying physics beyond the Standard Model. A first muon collider with variable
c.m.\ energy in the range $\sqrt s = 100$ to 500~GeV provides unique
opportunities for discovery and factory-like production of Higgs bosons in the
$s$-channel. For excellent (but achievable) machine energy resolution, the
total width and $\mupmum$ coupling of a SM-like Higgs boson with mass $\lsim
2\mw$ (as particularly relevant to supersymmetric/GUT models) can be directly
measured with substantial precision. Multiplication of measured branching
ratios by the total width yields the corresponding couplings. As a result, the
light CP-even SM-like Higgs of the minimal supersymmetric model can be
distinguished from the Higgs of the minimal Standard Model over a larger
portion of supersymmetric parameter space than otherwise possible. Scan
discovery and detailed measurements of total widths and some partial widths of
the heavier CP-even and CP-odd Higgs bosons of the minimal supersymmetric model
are possible for Higgs masses up to the maximum $\rts$. The excellent energy
resolution, absence of beamstrahlung and mild bremsstrahlung at the first muon
collider would allow increased precision for the measurement of $\mt$ and $\mw$
via $t\anti t$ and $\wp\wm$ threshold studies. A multi-TeV $\mm$ collider would
open up the realm of physics above the 1 TeV scale. Pair production of
supersymmetric particles up to masses even higher than consistent with
naturalness would be possible, guaranteeing that the heavier gauginos and
possibly very massive squarks would be abundantly produced and that their
properties could be studied. Very importantly, the multi-TeV collider would
guarantee our ability to perform a detailed study of a strongly-interacting

High Energy Physics - Phenomenology;High Energy Physics - Experiment