Cockroaches are members of the order Blattodea, which includes the termites, a group of insects once thought to be separate from cockroaches. Currently, there are 4,600 species described and over 460 genera worldwide.[1][2] The name "cockroach" comes from the Spanish word for cockroach, cucaracha, transformed by 1620s English folk etymology into "cock" and "roach".[3] The scientific name derives from the Latin blatta, "an insect that shuns the light", which in classical Latin was applied not only to cockroaches, but also to mantids.[4][5]

Historically, the name Blattaria was used largely interchangeably with the name Blattodea, but whilst the former name was used to refer to 'true' cockroaches exclusively, the latter also includes the termites. The current catalogue of world cockroach species uses the name Blattodea for the group.[1] Another name, Blattoptera, is also sometimes used.[6] The earliest cockroach-like fossils ("blattopterans" or "roachids") are from the Carboniferous period 320 million years ago, as are fossil roachoid nymphs.[7][8][9]

Since the nineteenth century, scientists believed that cockroaches were an ancient group of insects that had a Devonian origin, according to one hypothesis.[10] Fossil roachoids that lived during that time differ from modern cockroaches in having long external ovipositors and are the ancestors of mantises, as well as modern blattodeans. As the body, hindwings and mouthparts are not preserved in fossils frequently, the relationship of these roachoids and modern cockroaches remain disputed. The first fossils of modern cockroaches with internal ovipositors appeared in the early Cretaceous. A recent phylogenetic analysis suggests that cockroaches originated at least in the Jurassic.[10]

The evolutionary relationships of the Blattodea (cockroaches and termites) shown in the cladogram are based on Eggleton, Beccaloni & Inward (2007).[11] The cockroach families Lamproblattidae and Tryonicidae are not shown but are placed within the superfamily Blattoidea. The cockroach families Corydiidae and Ectobiidae were previously known as the Polyphagidae and Blattellidae.[12]