Geosynthetics are sheet polymericmaterials used in civil engineering. They have been used since the 1970s in geotechnical (soil) structures for functions such as separation, reinforcement, drainage, filtration, liquid containment and as gas barriers. In practice this has included applications as diverse as reinforcement in the walls of the Pentagon, reservoir liners, canal liners, road reinforcement, retaining walls, sports fields, dams, landfill liners, embankment stabilisation, tree containers, chemical tank liners, and as base and roofing membranes for new buildings. There is an increasing trend to use recyclates in geosynthetics, particularly PET from bottle recovery. Geosynthetics often play critical roles in civil engineering and it is important that the materials in use can withstand the physical and chemical pressures of the environment. These range from resistance to leachates from landfill to resistance to root damage in soil liners, as well as standard properties such as resistance to creep, oxidation and UV light, and tensile strength. This has resulted in sets of test standards being developed by the EU, ISO, BSI and ASTM. Dr Cook is an expert in the testing of geosynthetics and has covered this area in the review. There are several main categories of geosynthetics: geotextiles, geomembranes, geosynthetic clay liners, geogrids and geonets. This review discusses the polymers used in each type, production methods, test methods and applications. Geotextiles are permeable fabrics comprising around 75% of all geosynthetics. Globally, 1,400 million square metres are used each year and the trend in consumption is upwards.. Polypropylene comprises the bulk of this with polyester as the second most commonly used material, Polymer properties and economics decide on material choice. Natural fibres are being used where durability is less important. Geomembranes are thin flexible sheets with very low permeability. They are used as barriers to the passage of gases of liquids. Butyl rubber was the first material used, but now PVC and polyethylene are the most common materials. Uses include landfill odour control, facing of dams and reservoir liners. Geosynthetic clay liners are structures containing a clay layer and used as water barriers. Thus the main component is a clay mineral, bentonite. They can be used instead of geomembranes or as a second line of defence to geomembranes. Geogrids are sheets of tensile elements with a regular network of apertures, usually constructed of polyethylene, polypropylene or polyester. The most common use is for renforcement of unstable soil and waste masses. Geonets are composite grid constructions used for drainage capabilities. Usually a geotextile is used as the drainage core with an upper and lower section of geomembrane. The review is accompanied by around 400 abstracts from papers and books in the Rapra Polymer Library database, to facilitate further reading on this subject. A subject index and a company index are included. Key features… * Functions of geosynthetics * Properties * Test standards * Materials in use * Applications