  This working group report focuses on the physics potential of $\mu^+\mu^-$
colliders beyond what can be accomplished at linear $e^+e^-$ colliders and the
LHC. Particularly interesting possibilities include (i)~$s$-channel resonance
production to discover and study heavy Higgs bosons with $ZZ$ and $WW$
couplings that are suppressed or absent at tree-level (such as the $H$ and $A$
Higgs bosons of supersymmetric models), (ii)~study of the strongly interacting
electroweak sector, where higher energies give larger signals, and
(iii)~measurements of the masses and properties of heavy supersymmetric
particles.
