In a small window of phase space, chiral perturbation theory
can be used to make standard model predictions for tau decays
into two and three pions.
For $\tau\to2\pi\nu_\tau$, we give the analytical result for
the relevant form factor $F_V$ up to two loops,
then calculate the differential spectrum and compare with available
data.
For $\tau\to 3 \pi \nu_\tau$, we have calculated the hadronic matrix
element to one loop.
We discuss the decomposition of the three pion states into partition
states and
we give detailed predictions for the decay in terms of
structure functions.
We also compare with low energy predictions of meson dominance models.
Overall, we find good agreement, but also
some interesting discrepancies, which
might have consequences beyond the limit of validity
of chiral perturbation theory.
