Many interactions in nature are long range. As long range interactions, we refer to those in which parts of the system far away from each other interact considerably. An historical example of such systems are stars inside a galaxy or globular clusters. Typically, in such a system, a star is subjected to a force dominated by the ensemble of the other stars (long range) rather than, for example, the neighboring ones (short range). As a consequence, one expects a very different behavior (and often counter-intuitive) compared to what happens in the short-range interacting regime usually encountered in statistical physics textbooks. For example, in the thermodynamic equilibrium, there is nonequivalence of ensembles or a possible apparition of negative specific heat in the micro-canonical ensemble.