The second largest family of monocotyledons on a worldwide basis, but the first in importance both ecologically and economically, dominating all the ‘grasslands’ of the world and providing the grain and fodder which are staples of diet for both man and animals. Wheat, rice, maize and guinea corn are reported to cover half the world's land under food crops.

Grasses are annual or perennial rosette herbs, occurring in every kind of habitat. The long-lived bamboos are lignified and of tree-like dimensions, but there are quite a number of species, even annual ones, which reach 5 m or more in height and have cane-like stems. In habit, though plentifully branched, grasses may be compact and upright (tussock-forming), or trailing, creeping or decumbent, or extended by means of axillary shoots, which form stolons above ground or rhizomes underground. Descoings (1972) distinguishes five habits. Annuals lack stolons and rhizomes, but perennials may adopt any of these habits. New axillary shoots may be called tillers, and flowering shoots are known as culms, but all aerial shoots are basally branched and have a limited life span. Growth is sympodial and non-flowering shoots are relatively short lived.

The leaf blade, generally linear to lanceolate in outline, arises from an open sheath which encircles the stem and younger leaves closely. Venation is always parallel (convergent), the wider leaves appearing Commelina like.