This chapter discusses pests and diseases, which are important in terms of crop losses to food systems. What are the options, principles, and practices that allow people to manage these tests in a sustainable fashion? Pests range from weeds to elephants to pigs to insects to viruses. The focus lies on crop losses that occur in the field pre-harvest and extend until post-harvest. 60-90% of crops can be lost if farmers do nothing, but with some efforts, the actual incurred loss decreases to between 20-60%. You can kill pests, use pesticides to reduce past numbers, repel them, manage the micro environment to reduce favorability, place barriers, etc. Pesticides are most popular in the modern world, and are actually part of the problem. Integrated pest management asks farmers to use pesticides only when necessary and to rely on agronomic practices and other natural means to reduce the potency of pests that they’re contending with. Case study of the IR8 crop and the pesticide issues of the Green Revolution and farmer field schools, and the push-pull system in Kenya. Synthetic pesticides are often harmful to health and environment.