Legumes are indispensable for the supply of reactive nitrogen into organic farming systems due to their ability to fix atmospheric nitrogen. This reactive nitrogen is used by all arable crops in the rotation and forms the foundation of the protein supply for livestock. In conventional farming, legumes offer the potential to diversify crop rotations, especially those dominated by cereals which are often cereal intensive. In these cropping systems, legumes ‘break’ the sequence of cereal crops. One of the most important consequences of this break-crop effect is the interruption of the life cycle of crop-specific pathogens and the associated savings in pesticides. This review summarises the current state of knowledge on crop rotations with and without legumes. It presents and evaluates the agronomic, ecological and economic effects of the cultivation of large and small legume species as main or catch crops or as components in mixtures. The focus is on relevant publications in scientific journals as well as practice and research reports from 2010 - 2020, carried out in Germany or comparable climatic conditions. From this we derive the necessary research requirements for the subject areas of crop production (conventional and organic), plant protection, economy, ecology and climate protection.