Prairies are ecosystems where the dominant plants are grasses, but herbs and shrubs are significant plants of the prairie as well. Few to no trees are found on prairie. The term 'prairie' is generally applied to grasslands found in North America.

In the United States, the prairie region includes all or most of North and South Dakota, Nebraska, Kansas, and Oklahoma; as well as substantial portions of Montana, Wyoming, Colorado, New Mexico, Texas, Missouri, Iowa, Illinois, Indiana, Wisconsin, and Minnesota. In Canada, the prairie provinces include Manitoba, Saskatchewan, and Alberta.

The formation of prairies can be attributed to climate, fire, and grazing. Climatic factors include periodic drought, reduced precipitation, and temperature extremes. Prairie plants are adapted to fire and periodic fires favored them. Prairie plants are adapted to the large and small grazing animals found on the prairie.

Prairies are often divided into tallgrass, midgrass, and shortgrass prairies based on the grass height and species composition. With decreasing precipitation from east to west, the tallgrass prairie is found in the east, the shortgrass in the west, with the midgrass in between.