at the Universite Claude Bernard (Lyon I). From the beginning, the SSRG has involved the cooperation of colleagues from other universities inside and outside France; in addition to the editors of this volume, its Scientific Committee consists of D. Bennequin, P. Libermann, A. Lichnerowicz, C.-M. MarIe, J.-M. Morvan, P. Molino, and J.-M. Souriau. In particular, there have always been strong connections with the University of California at Berkeley, making this other "UCB" into a virtual fifth pole of the SSRG. Through its international meetings, of which the first five were held at Lyon, Montpellier, and Marseille, the SSRG has become an important cen­ ter of exchange for the latest developments in symplectic geometry and its applications. It seemed natural, therefore, to have this sixth meeting at MSRI in Berkeley in conjunction with the "symplectic year" 1988-89.