Stochastic thermodynamics is a recently established discipline of statistical physics.It explores fundamental aspects of non-equilibrium processes by applying and extending concepts from equilibrium thermodynamics to the non-equilibrium realm, typically on thelevel of single particle trajectories monitored over the entire system evolution. This approach provides an adequate framework to investigate the behaviour of ``small systems’’ on mesoscopic scales for which thermal fluctuations may have a significant or even dominant effect on the general system properties.We consider such small systems consisting of so-called Brownian particles (like colloids in suspension or biological macromolecules in a cell). After introducing the standard model for Brownian motion, we briefly describe the ideas and concepts leading to a (trajectory-wise) thermodynamic characterization of Brownian motion, and finally elaborateon central results from stochastic thermodynamics. As a refinement of the second law of thermodynamics, the most famous amongst these results are probably the fluctuation theorems.
