A conference, to celebrate the 65th birthday of Professor James Serrin, was held at the University of Ferrara from 26 to 30 October 1992, on the occasion of the sixth centenary of the foundation of the university. The dual purpose of this conference was to honor James Serrin and to bring together mathematicians in four main areas of Professor Serrin's research in- terests: partial differential equations, variational methods, fluid mechanics, and thermodynamics. These fields, with their significant historical connotation, still remain the object of active research and development, and possess a remarkable degree of interrelation in their pure and applied aspects. Thus the organizing committee, consisting of G. Buttazzo, G.P. Galdi, E. Lanconelli, and P. Pucci, had the opportunity to invite a number of well-known mathematicians and friends of James Serrin to make this meeting a success. An honorary committee was also formed, including Professor A. Rossi, Rector of the University of Ferrara, Professor C. Bighi, President of the Accadernia Scienze di Ferrara, Professor G. Del Piero, Decano of the Faculty of Engineering of the University of Ferrara, and Professor L. Zanghirati, Director of the Department of Mathematics of the University of Ferrara. The conference was further supported by G.N.A.F.A., G.N.F.M., and the Mathematics Committee of the Consiglio Nazionale delle Ricerche, together with the University of Ferrara and the Cassa di Risparrnio of Ferrara, to all of whom the organizing committee expresses their most sincere thanks.