  At FCC-ee, about $1.7 \times 10^{11}$ \mbox{Z $\to$ \texttau$^+$\texttau$^-$}
events will be produced. This high statistics in the clean e$^+$e$^-$
environment opens the possibility of much improved determinations of
\texttau-lepton properties and, via the measurement of the \texttau\
polarisation, of the neutral-current couplings of electrons and $\tau$s.
Improved measurements of \texttau-lepton properties -- lifetime, leptonic
branching fractions, and mass -- allow important tests of lepton universality.
The experimental challenge is to match as far as possible statistical
uncertainties generally at the $10^{-5}$ level. This applies in particular to
the lifetime measurement, which is derived from the \mbox{2.2-mm} \texttau\
average flight distance, and for the branching fraction and polarisation
measurements, where the cross-channel contamination is of particular concern.
These issues raise strict detector requirements, in particular, on the accuracy
of the construction and alignment of the vertex detector and of the precise
calorimetric separation and measurement of photons and \textpi$^0$s in the
collimated \texttau\ decay topologies.
