  Until present the study of the form factors associated to the vector and
axial-vector components of the hadronic weak current has been carried out with
a plethora of modelizations of the underlying strong interactions. While of
importance to get an understanding of the dynamics involved, the amount and
quality of the experimental data start to show some discrepancies with the
analysed models. Moreover, and from a theoretical point of view, most of these
models are not consistent with quantum chromodynamics (QCD). We propose a
QCD-based model-independent procedure to analyse those decays through the use
of the resonance chiral theory, the low-energy effective action of QCD in the
relevant resonance region. Within this framework we study the hadronic
off-shell width of the Rho meson and the vector form factor of the pion in
Tau(-) -> Pi(-) Pi(0) nu_tau. We also comment on the Tau(-) -> (Pi Pi Pi)(-)
nu_tau decay.
