This paper reviews recent developments in the understanding of the scrape-off layer structure.After the discussion of the general properties of a scrape-off layer formed by an axisymmetriclimiter the more common case of non-axisymmetry is analysed. Original results are presentedconcernng a three-dimensional model of the SOL and related experiments. In the high-density casea specific structdre develops, which may be described as a neutral cloud shielding the limiter.The role of a structured SOL for the accountability of energy and particle fluxes is shortly evaluated.