  This is a review of electroweak precision physics with particular emphasis on
low-energy precision measurements in the neutral current sector of the
electroweak theory and includes future experimental prospects and the
theoretical challenges one faces to interpret these observables. Within the
minimal Standard Model they serve as determinations of the weak mixing angle
which are competitive with and complementary to those obtained near the
Z-resonance. In the context of new physics beyond the Standard Model these
measurements are crucial to discriminate between models and to reduce the
allowed parameter space within a given model. We illustrate this for the
minimal supersymmetric Standard Model with or without R-parity.
