This volume is the 14 th and last one of the series "Nonlinear Partial
Differential Equations and their Applications. Coll~ge de France Seminar",
which published the texts of the lectures given at the seminars organized by
Jacques-Louis Lions, from his election at the Coll~ge de France in 1973 until
his retirement in 1998. It was one of the foremost seminars in nonlinear
PDE's and their applications during that period.
It is unfortunate that because of his untimely death, on May 17,
2001, Jacques-Louis Lions will not see its publication. This volume is
dedicated to his memory.