  The use of Pade approximants for the description of QCD matrix elements is
discussed in this talk. We will see how they prove to be an extremely useful
tool, specially in the case of resonant amplitudes. It will allow the inclusion
of high-energy Euclidian data to improve the determination of low-energy
properties, such as the quadratic vector radius. This does not mean that the
rational approximations can be arbitrarily employed for the extraction of any
desired hadronic parameter. A discussion about the validity, limitations and
possible issues of the Pade analysis is carried on along the paper. Finally,
based on the de Montessus de Ballore's theorem, a theoretically safe new
procedure for the extraction of the pole mass and width of resonances is
proposed here and illustrated with the example of the rho(770).
