Recurrent novae are those novae known to have had at least two outbursts within a century. I review here the mai characteristics of these objects in the Local Group, selecting criteria for a basic classification, and discussing both the state of theoretical modeling and initial statistics in external galaxies. Generally, recurrent novae in short period systems with unevolved companions have quite slow outbursts, whereas the outbursts in RN with evolved secondaries evolve very quickly, and there is evidence that they host very massive white dwarfs. I discuss in detail some of the X-ray gratings observations of recurrent novae in the Local Group, demonstrating what can be learned from them. The most important parameter that can be derived is the effective temperature of the white dwarf, which is directly connected with its mass.