A critical step in the development of a robust Agrobacterium tumefaciens -mediated transformation �system for cereal crop plants is the establishment of optimal conditions for efficient T-DNA delivery into target tissue, from which plants can be regenerated. Although, Agrobacterium -mediated transformation of cereals is an important method that has been widely used by many laboratories around the world, routine protocols have been established only in specific cultivars within a species and with specific tissues of high regeneration potential. Cocultivation of highly embryogenic callus tissue or healthy immature embryos with A. tumefaciens is considered one of the critical factors in successful genetic transformation of crop plants. Immature embryos collected only from vigorously growing healthy and green plants grown in the field or in the well-conditioned greenhouse are the ideal target for genetic transformation of recalcitrant crop species. Here, we describe an Agrobacterium -mediated transformation method that uses immature embryos as the starting material for inoculation with Agrobacterium . The aim of this chapter is to provide the key steps/components involved in Agrobacterium -mediated transformation of cereal crops. However, these steps or components often vary between protocols and from laboratory to laboratory, and can be optimized or modified based on the requirement of a specific cultivar or species.