  If supersymmetry (SUSY) is realized at the electroweak scale, its underlying
structure and breaking mechanism may be explored with great precision by a
future linear $e^+ e^-$ collider (LC) with a clean environment, tunable
collision energy, high luminosity polarized beams, and additional $e^-e^-$,
$e\gamma$ and $\gamma\gamma$ modes. We review a few recent developments for
determining fundamental SUSY and Higgs parameters, measuring CP violating $H/A$
mixing in the decoupling regime and probing the next--to--minimal
supersymmetric standard model at the LC.
