Testing supersymmetry at the Next Linear Collider.

Up to now, almost all discussion of supersymmetry at future colliders has been concerned with particle searches. However, if candidates for supersymmetric particles are found, there is much more that we will want to know about them. Supersymmetry predicts quantitative relations among the couplings and masses of supersymmetric particles. We discuss the prospects for testing such relations at a future ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{\ensuremath{-}}}$ linear collider, using measurements that exploit the availability of polarized beams. Precision tests from chargino production are investigated in two representative cases, and sfermion and neutralino processes are also discussed.