Rice is the major staple food for hundreds of millions of people. It is generally consumed in its milled form with outer layers (pericarp, tegmen and aleurone layers) removed. The main reason for milling is to remove the oil-rich aleurone layer, which turns rancid upon storage, especially in tropical and subtropical areas. As a result, the edible part of rice grains consists of the endosperm, filled with starch granules and protein bodies, but it lacks several essential nutrients for the maintenance of health, such as carotenoids exhibiting provitamin A-activity. Thus, reliance on rice as a primary food staple contributes to vitamin A deficiency, a serious public health problem in at least 26 countries including highly populated areas of Asia, Africa and Latin America A complementary intervention to existing strategies for reducing vitamin A deficiencies in the highest-risk countries is to fortify the major staple food, rice, with provitamin A through plant breeding. This can only be achieved by recombinant technologies rather than by conventional breeding, due to the lack of any rice cultivars producing this provitamin in the endosperm. Both because the transformation of rice is well-established and because the entire carotenoid biosynthetic pathway has been molecularly identified recently, it seemed feasible to introduce the complete provitamin A (β-carotene) biosynthetic pathway into rice endosperm by genetic engineering.