These seminar notes contain a brief introduction into the principles of stochastic thermodynamics and some of its recent ramifications from a personal perspective. Thermodynamic concepts like work, exchanged heat and entropy production can consistently be defined on the level of individual fluctuating trajectories taken from either a time‐dependent or a non‐equilibrium steady state ensemble. Fluctuation theorems constrain the probability distributions for these thermody‐namic quantities. For systems containing fast internal degrees of freedom the crucial distinction between internal and free energy for a correct identification of both dissipated heat and system entropy is emphasized. For non‐equilibrium steady states, a generalized fluctuation‐dissipation theorem relates the response to a small perturbation to correlation functions in the steady state involving observables expressing the various contributions to entropy production along the trajectory.