This volume contains the proceedings of a NATO Advanced Study Institute devoted to the study of dynamical correlation functions of the form (I) J e-lwt 6ft T- is an equilibrium average. In equation (1) it is useful to regard the product AB as the product of two operators in cases in which A and B refer to different spatial points in a condensed matter sys tem and/or in which A and B behave dynamically in a quasiharmonic way. In the second case, one has a two quasiparticle correlation function and CAB;AB(w) gives information about quasiparticle inter actions. Condensed matter physics has...