1. The optimal transportation problem - Optimal transportation on non-compact manifolds, costs obtained from Lagrangians, interpolation and absolute continuity, displacement convexity.- 2. The irrigation problem - Dynamic cost on traffic plans, syncronization, stability.- 3. Variational models for the incompressible Euler equations - Arnold's least action problem, Brenier's variationals models, gap phenomena, necessary and sufficient optimality conditions, regularity of the pressure.- 4. On the structure of the Aubry set and Hamilton-Jacobi equation - Structure of the Mather quotient set, estimate of its Hausdorff dimensions, applications in dynamics.