Crop rotations, green manures, and cover crops are the foundations of good farming. Crop rotation provides diversity that results in resilience, green manures cycle nutrients by feeding soil microbes, and cover crops protect the soil from erosion and nutrient loss. These practices ultimately result in soil aggregation, an essential principle of sustainable farming. This publication focuses on green manure and cover crops. To impart a sense of the importance of these practices in sustainable farming, it summarizes the effect of cover crops and green manures on organic matter and soil structure, soil microbial activity, nitrogen production, and soil and water conservation. It addresses management practices including green manuring, cover crop systems, termination to create a cover crop mulch, planting green, cover crops in high tunnels, the limitations of cover crops, and the economics of cover crops. This publication also provides a selection of resources for further reading, including regional resources and cover crop databases.