  Sufficiently inclusive observables in the decay of the tau lepton can be
calculated using the methods of perturbative QCD. These include the asymmetry
parameter $A_\tau$ that determines that angular distribution of the total
hadron momentum in the decay of a polarized tau. It should be possible to
measure $A_\tau$ accurately using existing data from LEP. Reliable estimates of
theoretical errors are essential in order to determine whether a given
observable is sufficiently inclusive to be calculated using perturbative
methods. The theoretical uncertainties due to higher orders in $\alpha_s$ can
be estimated using recent calculations to all orders in the large-$(33-2N_f)$
limit. These estimates indicate that tau decay data can be used to determine
$\alpha_s(M_Z)$ to a precision of 2% or better.
