Symmetries of QCD

The distinction between charges defined at a fixed time and those specified on a null plane is briefly discussed. The talk then addresses the approximate flavour symmetries of QCD that arise because some of the quarks happen to be light. In particular, the role of the quark condensate for the low energy structure of QCD, the dependence of Mπ on mu and md and the low energy theorems for the ππ scattering amplitude are reviewed. The new data on Ke4 decay beautifully confirm the standard picture, according to which the quark condensate is the leading order parameter of the spontaneously broken chiral symmetry