Dunes are very variable formations. They constitute particular ecosystems in all geographic areas of the earth. Continental or inland dunes are found in dry and uncovered areas whereas littoral dunes exist along the coastal marine fringe. Also, fossile marine dunes can be found in humid areas. Within these variations, important relations and differences are found. On the one hand, their ecological situation (removal and accretion of substrate, erosion mechanics, relations of humidity and temperature and floristic composition) while on the other, their historical development in relation to the time factor. Different and numerous succesional stages which influence their biocenosis can be found. A classification of the dune system is, in itself, quite difficult. However, regional examples that can be defined better exist. At present and in many places, dunes have been greatly modified by the influence of humans (use of land, tourism, etc.). The efforts being made to protect them are aimed at stabilizing their ecosystems. Examples of dunes in Europe, Arabia and Africa are given. Also, impressions concerning the relief of dunes, their importance as specific living areas and problems of their conservation and recuperation are discussed.