Tau as a Probe for New Physics

The usage of polarimetry and spin-correlation tests to determine the {\em complete Lorentz structure} of the tau lepton’s charged and neutral-current couplings is reviewed. The emphasis is on tests for something'' in a $(V-A) + $ something’’ structure in ${J^{Charged}}_{Lepton}$ current, so as to bound the scales $\mathrm{\Lambda }$ for ``new physics" such as arising from tau weak magnetism, weak electricity, and/or second-class currents. Tests for $T$ and for $CP$ violation are discussed.