  In this review, an outline of the so called Freidlin-Wentzell theory and its
recent extensions is given. Broadly, this theory studies the exponential rate
at which the probabilities of rare events related to random perturbation of ODE
decays. The typical situation is when an ODE has several stable equilibria, in
which case, the theory predicts the most likely paths in which the randomly
perturbed system goes from one equilibria to another. In recent developments I
will outline how recent approaches allows to distinguish between paths that are
otherwise exponentially equivalent and provide an overview of applications of
this theory. In particular, we outline the influence of this theory in Monte
Carlo Algorithms and Simulated Annealing schemes.
