The high penetration of distributed generators, most of them based on renewable energy sources, is modifying the traditional structure of the electric distribution grid. If the power of distributed generators is high enough to feed the loads of a certain area, this area could be disconnected from the main grid and operate in islanded mode. Microgrids are composed by distributed generators, energy storage devices, intelligent circuit breakers and local loads. In this paper, a review of the main microgrid architectures proposed in the literature has been carried out. The microgrid architectures are first classified regarding their AC or DC distribution buses. Besides, more complex microgrid architectures are shown. Both advantages and disadvantages of each one of the microgrid families are discussed.