The theory of Large Deviations deals with techniques for estimating probabilities of rare events. These probabilities are exponentially small in a natural parameter and the task is to determine the exponential constant. To be precise, we will have a family Pn of probability distributions on a space X and asymptotically Pn (A) = exp [-n inf/xεA I(x) + o(n) (equation presented) for a large class of sets, with a suitable choice of the function I(x). This function is almost always related to some form of entropy. There are connections to statistical mechanics as well as applications to the study of scaling limits for large systems. The subject had its origins in the Scandinavian insurance industry where it was used for the evaluation of risk. Since then, it has undergone many developments and we will review some of the recent progress.