Cover crops (CCs) are close-growing crops providing protection for soil and seeding between periods of normal crop production. They are positioned in rotation between two main or cash crops, and not primarily grown for harvest. Although traditionally CCs have been terminated and incorporated into the soil, the emergence of conservation agriculture and no-till systems has led to greater emphasis on retaining CC residues as a precrop mulch for the following crop. This chapter considers recent research on the benefits of CCs in areas such as erosion and soil structure, nutrient cycling and control of weeds, diseases and pests. It then looks at the broader role of CCs in promoting biodiversity, and their role in carbon sequestration and reducing GHGs. Finally, it discusses some of the challenges in using CCs to optimize crop yields, and presents a number of key questions for the future of this practice.