Semileptonic decays of polarised $\tau$ leptons are investigated.
Predictions for the rate, based on CVC and chiral Lagrangians, are
contrasted with experiments. Predictions for the angular distributions
of three meson final states are given. Emphasis is put on studies in
electron-positron annihilation where the neutrino escapes detection and
the $\tau$ restframe cannot be reconstructed. It is shown that the
form factors can be measured in ongoing high statistics experiments.
Of particular interest for the three meson case are the distribution
of the normal to the Dalitz plane and the distribution around this
normal. At LEP these distributions allow for an improved measurement of
the $\tau$ polarisation. Implications are considered for an experiment
where the $\tau$
restframe is reconstructed. It is shown that the measurement of impact
parameters with the help of vertex detectors allows a full kinematic
reconstruction, including the direction of the $\tau$ and the missing
neutrino momentum.