Cover crops could be considered the backbone of any annual cropping system that seeks to be sustainable. This publication summarizes the principal uses and benefits of cover crops and green manures. Brief descriptions and examples are provided for winter cover crops, summer green manures, living mulches, catch crops, and some forage crops. To impart a sense for the importance of these practices in sustainable farming, it summarizes the effect of cover crops and green manures on organic matter and soil structure, nitrogen production, soil microbial activity, nutrient enhancement, rooting action, weed suppression, and soil and water conservation. Management issues addressed include vegetation management, limitations of cover crops, use in crop rotations, use in pest management, and economics of cover crops.