The use of woven and non-woven synthetic membranes in geotechnology is now recognized. Their use in a great number of projects (such as highways, earthworks, drainage and dams) depends on the mechanical and hydraulic properties of soil/membrane systems. This article includes a summary description of the various geotextiles in use and their various applications. It also lists the properties on which different uses of geotextiles are based. Lastly, it describes work now being carried out at the Ecole Polytechnique. -- AATA