After introducing the concept of effective field theories, the Standard Model is considered at energies below 1 GeV. The spontaneous breaking of the approximate chiral symmetry of QCD is a main ingredient of chiral perturbation theory, the nonrenormalizable effective field theory of the Standard Model at low energies. The main features of chiral perturbation theory are discussed. In addition to a brief survey of applications for strong and electroweak processes, elastic pion pion scattering and several kaon decays are treated in more detail. The theoretical precision attained in some of these examples is remarkable for hadronic processes at low energies where the usual perturbative treatment fails.
