Rice is the world's most important food crop, providing a primary food source for over a third of the global population. Over 90% of the world's rice is grown and consumed in Asia, where 60% of the world's population lives. Rice accounts for 35 to 60% of the calories consumed by 3 billion Asians. It is planted on about 148 million hectares annually, or 11% of the world's cultivated land. In 1996, world rice production was 553 million tons, with China as the largest producer, followed by India, Indonesia, Bangladesh, Vietnam, Thailand, and Myanmar. Rice is grown in diverse ecosystems, including irrigated, rainfed lowland, rainfed upland, and flood-prone areas. Human selection and adaptation have led to numerous cultivars, with an estimated 120,000 rice varieties worldwide. Since the establishment of the International Rice Research Institute (IRRI) in 1960, rice varietal improvement has intensified, leading to the development of high-yielding varieties now planted on 70% of the world's riceland. Rice production doubled between 1966 and 1990 due to the adoption of improved varieties. To feed the growing population, rice production must increase by 60% by 2025. Rice has a complex origin, with O. sativa, the Asian cultivated rice, originating from a common ancestor with an AA genome. The perennial and annual ancestors of O. sativa are O. rufipogon and O. nivara, while those of O. glaberrima are O. longistaminata, O. breviligulata, and O. glaberrima. Indica and japonica rices have a polyphyletic origin, with indicas likely domesticated in the Himalayas and japonicas in South China. Indica rices dispersed throughout the tropics and subtropics, while japonica rices moved northward to become temperate ecotypes and southward to Southeast Asia, West Africa, and Brazil, becoming tropical ecotypes. New tools in molecular and cellular biology, such as anther culture, molecular marker-assisted selection, and genetic engineering, will play an increasing role in rice improvement. Rice is also an important staple in Latin America, Africa, and the Middle East, and is consumed in various forms, including polished and unpolished varieties. Brown rice, though more nutritious in some aspects, is less stable for storage and may be less nutritious than white rice.Rice is the world's most important food crop, providing a primary food source for over a third of the global population. Over 90% of the world's rice is grown and consumed in Asia, where 60% of the world's population lives. Rice accounts for 35 to 60% of the calories consumed by 3 billion Asians. It is planted on about 148 million hectares annually, or 11% of the world's cultivated land. In 1996, world rice production was 553 million tons, with China as the largest producer, followed by India, Indonesia, Bangladesh, Vietnam, Thailand, and Myanmar. Rice is grown in diverse ecosystems, including irrigated, rainfed lowland, rainfed upland, and flood-prone areas. Human selection and adaptation have led to numerous cultivars, with an estimated 120,000 rice varieties worldwide. Since the establishment of the International Rice Research Institute (IRRI) in 1960, rice varietal improvement has intensified, leading to the development of high-yielding varieties now planted on 70% of the world's riceland. Rice production doubled between 1966 and 1990 due to the adoption of improved varieties. To feed the growing population, rice production must increase by 60% by 2025. Rice has a complex origin, with O. sativa, the Asian cultivated rice, originating from a common ancestor with an AA genome. The perennial and annual ancestors of O. sativa are O. rufipogon and O. nivara, while those of O. glaberrima are O. longistaminata, O. breviligulata, and O. glaberrima. Indica and japonica rices have a polyphyletic origin, with indicas likely domesticated in the Himalayas and japonicas in South China. Indica rices dispersed throughout the tropics and subtropics, while japonica rices moved northward to become temperate ecotypes and southward to Southeast Asia, West Africa, and Brazil, becoming tropical ecotypes. New tools in molecular and cellular biology, such as anther culture, molecular marker-assisted selection, and genetic engineering, will play an increasing role in rice improvement. Rice is also an important staple in Latin America, Africa, and the Middle East, and is consumed in various forms, including polished and unpolished varieties. Brown rice, though more nutritious in some aspects, is less stable for storage and may be less nutritious than white rice.