  We discuss the possibilities of extracting the constraints on New Physics by
using the current data on the leptonic and semileptonic decays of pseudoscalar
mesons. In doing so we use a general low energy Lagrangian that besides the
vector and axial operators also includes the (pseudo-)scalar and tensor ones.
In obtaining constraints on New Physics couplings we combine the experimental
information concerning several decay modes with the accurate lattice QCD
results for the hadronic matrix elements. We propose to study new observables
that can be extracted from the angular analysis of the semileptonic decays and
discuss their values both in the Standard Model and in some specific scenarios
of physics beyond the Standard Model.
