The celebrated fluctuation relations (Crook's fluctuation theorem, Jarzinsky's identity, Gallavotti-Cohen symmetry etc.) express the time-irreversibility of an open system's evolution and link it to thermodynamic quantities such as entropy production, dissipated work etc. In a way, they provide stochastic formulations of the Second Law of thermodynamics. In this lecture I will provide the simplest possible derivation of fluctuation relations and discuss the possibility of generalizing them in the case where the observer has partial information about the system. I will also briefly touch on the formulation of fluctuation relations for quantum systems.