Light Quark Masses
  Lecture Notes, Summer School on Masses of Fundamental Particles, Cargese, 1996. In the first part, some qualitative aspects the mass pattern are discussed, concerning the breaking of isospin and eightfold way symmetries. The second part deals with the chiral perturbation theory results for the masses of the pseudoscalar octet, which lead to very stringent constraints for the relative size of the light quark masses. 
H. Leutwyler (University of Bern and CERN)