Calcareous grassland (or alkaline grassland) is an ecosystem associated with thin basic soil, such as that on chalk and limestone downland.^[1] Plants on calcareous grassland are typically short and hardy, and include grasses and herbs such as clover. Calcareous grassland is an important habitat for insects, particularly butterflies and ants,^[2] and is kept at a plagioclimax by grazing animals, usually sheep and sometimes cattle. Rabbits used to play a part but due to the onset of myxomatosis their numbers decreased so dramatically that they no longer have much of a grazing effect.

There are large areas of calcareous grassland in northwestern Europe, particularly areas of southern England, such as Salisbury Plain and the North and South Downs.

The machair forms a different kind of calcareous grassland, where fertile low-lying plains are formed on ground that is calcium-rich due to shell sand (pulverised sea shells).