  We review a variety of topics related to hadronic structure functions in
exclusive semihadronic tau decays. We introduce the concept of structure
functions and summarize the most important concepts. We then calculate the
decay $\tau \to 3 \pi \nu_\tau$ for very small hadronic invariant mass to one
loop in Chiral Perturbation Theory. New interesting features emerge with
respect to the known results at tree level, in particular for the structure
functions $w_D$ and $w_E$. We discuss the prospects for experimental
verification of our predictions. Finally, we discuss various issues at higher
$Q^2$, related to hadronic resonance physics. Here we consider $2\pi$, $\pi K$,
$3 \pi$, $K \pi K$ and $\pi K \pi$ hadronic final states.
