  Low energy precision experiments provide significant tests of the laws of
nature that can reveal physics beyond the Standard Model. A good theoretical
understanding of the low energy properties of QCD is required for this purpose.
The recent developments at the interface between lattice and effective field
theory methods provide an excellent basis for pion physics already now, while
the extension required to explore the low energy properties in the strange
quark sector yet calls for further work, also in view of a better determination
of the light quark masses.
  At the precision achieved in lattice determination of quark mass ratios, the
e.m. self-energies of the mesons play an important role. I point out some
unresolved issues occurring in this context and then summarize the present
knowledge of the light quark masses.
