  We employ a mathematical framework based on rational approximants in order to
calculate meson form factors. The method profits from unitary, is systematic
and data based, and is able to ascribe a systematic uncertainty which provides
for the desired model independence. Two examples are discussed: the transition
form factor entering the pseudoscalar-pole piece of the hadronic light-by-light
contribution to the anomalous magnetic moment of the muon, and the $B \to \pi$
form factor participating the $B\to\pi\ell\nu_{\ell}$ differential branching
ratios which allows to determine the $|V_{ub}|$ CKM parameter.
