1. Introduction, plan of the lectures, Poisson structures; 2. Poisson structures on finite-dimensional manifolds, Hamiltonian systems, completely integrable systems; 3. Classical analogue of the Dirac monopole, complete integrability and algebraic geometry; 4. Poisson structures on loop spaces, systems of hydrodynamic type and differential geometry; 5. Non-linear WKB method, hydrodynamics of weakly deformed soliton lattices; References.