Cereals are food security crops because of their high nutritive values for energy (carbohydrate-based energy) and other nutrients (proteins) and their long-term storability. They constitute the main food staples in many parts of the world and are primary animal feed ingredients. Cereal production is lost and wasted due to insects and fungal infestations. For the latter, fungi cause cereal losses by reducing grain yields, by spoiling cereals and rendering them unfit for human and animal consumption, or by production of secondary metabolites like mycotoxins, which are harmful to humans and animals. This chapter will focus on fungal ecology and storage fungal contamination in three major types of cereals (maize, wheat, and rice) which constitute more than 90% of total world cereal production.