Table of contents : Introduction....Pages 1-6 Notations and basic facts on center manifolds....Pages 9-16 The linear theory....Pages 17-26 Hamiltonian flows on center manifolds....Pages 27-40 Hamiltonian systems with symmetries....Pages 41-59 Lagrangian systems....Pages 61-83 Nonautonomous systems....Pages 85-92 Elliptic variational problems on cylindrical domains....Pages 95-102 Capillarity surface waves....Pages 103-108 Necking of strips....Pages 109-119 Saint-Venant's problem....Pages 121-131