  Precise measurements of the lepton properties provide stringent tests of the
Standard Model and accurate determinations of its parameters. We overview the
present status of tau physics, highlighting the most recent developments, and
discuss the prospects for future improvements. The leptonic decays of the tau
lepton probe the structure of the weak currents and the universality of their
couplings to the W boson. The universality of the leptonic Z couplings has also
been tested through leptonic Z decays. The hadronic tau decay modes constitute
an ideal tool for studying low-energy effects of the strong interaction in very
clean conditions. Accurate determinations of the QCD coupling and the Cabibbo
mixing have been obtained with tau data. The large mass of the tau opens the
possibility to study many kinematically-allowed exclusive decay modes and
extract relevant dynamical information. Violations of flavour and CP
conservation laws can also be searched for with tau decays. Related subjects
such as muon decays, the electron and muon anomalous magnetic moments, neutrino
mixing and B-meson decays into tau leptons are briefly covered. Being one the
fermions most strongly coupled to the scalar sector, the tau lepton is playing
now a very important role at the LHC as a tool to test the Higgs properties and
search for new physics at higher scales.
