Viviane Baladi, Brigitte Vallee Euclidean algorithms are Gaussian (756K, postscript) ABSTRACT. We obtain a Central Limit Theorem for a class of costs associated to three standard Euclidean algorithms, with optimal speed of convergence. For lattice costs, we establish a Local Limit Theorem, with optimal speed of convergence. We view an algorithm as a dynamical system and combine tools imported from dynamics, such as transfer operators, with various other techniques. To obtain estimates on transfer operators when a parameter varies along vertical lines in the complex plane, we adapt techniques introduced by Dolgopyat in the context of continuous-time dynamics.