Successful revegetation projects rely on the use of high quality seed. Seed from harvesting machines or hand collections will include a mix of stems, leaves, chaff, appendages, empty glumes, and seeds of various sizes and quality. The extraneous materials must be removed to insure a quality product and to allow uniform dispensing through seeding equipment. This chapter deals primarily with machinery used by USDA NRCS Plant Material Centers (PMC) and researchers. Manufacturers have developed numerous seed cleaning devices for small lots as well as very large lots. With experience and some ingenuity, operators can adjust the cleaning machinery to produce a quality seed product with high purity levels. Pre-cleaning is the rapid removal of excessive, extraneous materials by scalpers, hammermills, or debearders prior to basic cleaning with air-screen separators. The air-screen separator, properly adjusted, can supply a finished product for many grasses, forbs, and shrubs. However, finishing machines are also available to separate seed by density, length, width, thickness, and shape. These include specific gravity separators, pneumatic separators, velvet rolls, spiral and indent cylinders, indent disks, magnetic separators, electrostatic separators, vibrator separators, stoners, fresh fruit separators, and others. Moisture content may be high in freshly harvested seed and drying may be required prior to cleaning. Processed seed should remain viable for several years if stored in a clean facility where temperature and humidity are kept low.