Title : "Second Law of Thermodynamics at finite times" Abstract: I shall discuss a finite-time refinement of the Second Law of Thermodynamics for Langevin stochastic processes describing mesoscopic systems driven by conservative or non-conservative forces and interacting with thermal noise. For overdamped dynamics, the refinement is based on the Monge-Kantorovich optimal mass transport. An application to a model of a micron-size particle manipulated by optical tweezers will serve as an illustration of the theory. Based on a joint work with E. Aurell, C. Mejía -Monasterio, R. Mohayaee and P. Muratore-Ginanneschi.