  The remarkable recent progress in the precision of Lattice QCD computations
for a number of physical quantities relevant for flavour physics has motivated
the introduction of isospin-breaking effects, including in particular
electromagnetic corrections, to the computations. The isospin breaking
corrections are necessary to fully exploit this improved precision for the
determination of the fundamental parameters of the Standard Model, including
the CKM matrix elements, and to look for deviations from experimental
measurements which might signal the presence of new physics. Together with
colleagues from Rome, we have developed and implemented a framework for
including isospin-breaking corrections in leptonic decays
$P\to\ell\bar\nu_\ell(\gamma)$, where $P$ is a pseudoscalar meson and $\ell$ a
charged lepton, and the theoretical framework and numerical results are
reviewed below. The status of our studies to extend this framework to
semileptonic decays $P_1\to P_2\ell\bar\nu_\ell(\gamma)$, where $P_{1,2}$ are
pseudoscalar mesons, is also presented.
