Cereal crops are mostly grasses cultivated for their edible grains or seeds (actually a fruit called a caryopsis). Cereal grains are grown in greater quantities worldwide than any other type of crop and provide more food energy to the human race than any other crop. In some developing nations, cereal grains constitute practically the entire diet of common folk. In developed nations, cereal consumption is more moderate but still substantial. The word cereal derives from Ceres, the name of the Roman goddess of harvest and agriculture. Grains are traditionally called corn in the United Kingdom, though that word became specified for maize in the United States, Canada, New Zealand, and Australia.

Cereal grains supply most of their food energy as starch. They are also a significant source of protein, though the amino acid balance is not optimal. Whole grains (see below) are good sources of dietary fiber, essential fatty acids, and other important nutrients. Rice is eaten as cooked entire grains, although rice flour is also produced. Oats are rolled, ground, or cut into bits (steel-cut oats) and cooked into porridge. Most other cereals are ground into flour or meal, that is milled. The outer layers of bran and germ are removed (see seed). This lessens the nutritional value but makes the grain more resistant to degradation and makes the grain more appealing to many palates. Health-conscious people tend to prefer whole grains, which are not milled. Overconsumption of milled cereals is sometimes blamed for obesity. Milled grains do keep better because the outer layers of the grains are rich in rancidity-prone fats. The waste from milling is sometimes mixed into a prepared animal feed. Once (optionally) milled and ground, the resulting flour is made into bread, pasta, desserts, dumplings, and many other products. Besides cereals, flour is sometimes made from potatoes, chestnuts and pulses (especially chickpeas).