Recent estimates (Kevan 1982; Günther, 1980, 1992; Otte 1994-1995; subsequent literature) indicate some 2400 valid Caeliferan genera and about 11000 valid species described to date. Many undescribed species exist, especially in tropical wet forests. The Caelifera are predominantly tropical, but most of the superfamilies are represented world wide.

By insect standards the Caelifera are relatively homogenous; all have jumping back legs and are almost exclusively herbivorous. None the less they show considerable diversity. As adults they range in size from a few millimetres to more than 15 cm in length, are flighted or flightless, occupy virtually all non-marine habitats in which plants can live (including deserts, water surfaces, the crowns of forest trees, grasslands, or underground); they eat algae, mosses, the leaves and reproductive organs of ferns, gymnosperms and angiosperms, or even the roots of the latter, with all degrees of foodplant specialisation from wide-range polyphagy to strict monophagy.

The Caelifera are probably the oldest living group of chewing folivorous insects. The Tettigonioidea may predate them geologically, but it is unclear how herbivorous these were, as many Tettigonioids are even now still carnivorous or omnivorous. The fossil Caelifera are reviewed by Zeuner (1941-1944), Sharov (1971), Kukalova-Peck (1991), Carpenter (1992) and Ross & Jarzembowski (1993). The split between the Caelifera and the Ensifera is not more recent than the Permo-Triassic boundary (Zeuner 1939). The earliest known representatives of an extant Caeliferan Superfamily are the extinct *Regiatidae (Tridactyloidea) from the Lower Jurassic (Gorochov 1995). Essentially modern Eumastacids are known from the mid-Jurassic, modern Tridactyloids and Tetrigoids from the early Cretaceous, Acridoids from the Eocene. Most, possibly all, of the modern superfamilies probably developed in the Jurassic.