Production data on cereals relate to crops harvested for dry grain only. Cereal crops harvested for hay or harvested green for food, feed, or silage and those used for grazing are excluded. Development relevance: The Food and Agriculture Organization (FAO) estimates that cereals supply 51 percent of Calories and 47 percent of protein in the average diet. The total annual cereal production globally is about 2,500 million tons. FAO estimates that maize (corn), wheat and rice together account for more than three-fourths of all grain production worldwide. In developed countries, cereal crops are universally machine-harvested, typically using a combine harvester, which cuts, threshes, and winnows the grain during a single pass across the field. In many industrialized countries, particularly in the United States and Canada, farmers commonly deliver their newly harvested grain to a grain elevator or a storage facility that consolidates the crops of many farmers. In developing countries, a variety of harvesting methods are used in cereal cultivation, depending on the cost of labor, from small combines to hand tools such as the scythe or cradle. Crop production systems have evolved rapidly over the past century and have resulted in significantly increased crop yields, but have also created undesirable environmental side-effects such as soil degradation and erosion, pollution from chemical fertilizers and agrochemicals and a loss of bio-diversity. Factors such as the green revolution, has led to impressive progress in increasing cereals yields over the last few decades. This progress, however, is not equal across all regions. Continued progress depends on maintaining agricultural research and education. The cultivation of cereals varies widely in different countries and depends partly upon the development of the economy. Production depends on the nature of the soil, the amount of rainfall, irrigation, quality of seeds, and the techniques applied to promote growth. Limitations and exceptions: Data on cereal production may be affected by a variety of reporting and timing differences. Millet and sorghum, which are grown as feed for livestock and poultry in Europe and North America, are used as food in Africa, Asia, and countries of the former Soviet Union. So some cereal crops are excluded from the data for some countries and included elsewhere, depending on their use. The data are collected by the Food and Agriculture Organization (FAO) of the United Nations through annual questionnaires and are supplemented with information from official secondary data sources. The secondary sources cover official country data from websites of national ministries, national publications and related country data reported by various international organizations. The FAO tries to impose standard definitions and reporting methods, but complete consistency across countries and over time is not possible. Thus, data on agricultural land in different climates may not be comparable. For example, permanent pastures are quite different in nature and intensity in African countries and dry Middle Eastern countries. The data collected from official national sources. Statistical concept and methodology: A cereal is a grass cultivated for the edible components of their grain, composed of the endosperm, germ, and bran. Cereal grains are grown in greater quantities and provide more food energy worldwide than any other type of crop; cereal crops therefore can also be called staple crops. Cereals production data relate to crops harvested for dry grain only. Cereal crops harvested for hay or harvested green for food, feed, or silage and those used for grazing are excluded. The Food and Agriculture Organization (FAO) allocates production data to the calendar year in which the bulk of the harvest took place. Most of a crop harvested near the end of a year will be used in the following year.