Atomic parity violation as a probe of new physics

Effects of physics beyond the standard model on electroweak observables ares studied using the Peskin-Takeuchi isospin-conserving, S, and -breaking, T, parametrization of ``new'' quantum loop corrections. Experimental constraints on S and T are presented. Atomic parity-violating experiments are shown to be particularly sensitive to S with existing data giving S=-2.7+/-2.0+/-1.1. That constraint has important implications for generic technicolor models which predict S~=0.1N_TN_D (N_T is the number of technicolors, N_D is the number of technidoublets).