Under the Whyte notation for the classification of steam locomotives, 2-2-2 represents the wheel arrangement of two leading wheels on one axle, two powered driving wheels on one axle, and two trailing wheels on one axle. The wheel arrangement both provided more stability and enabled a larger firebox than the earlier 0-2-2 and 2-2-0 types. This wheel arrangement is sometimes described as a Single, although this name could be used to describe any kind of locomotive with a single pair of driving wheels.

Other equivalent classifications are:

The 2-2-2 configuration appears to have been developed by Robert Stephenson & Company in 1834, as an enlargement of their 2-2-0 Planet configuration, offering more stability and a larger firebox. The new type became known as Stephenson's Patentee locomotive. Adler, the first successful locomotive to operate in Germany, was a Patentee supplied by Robert Stephenson & Company in component form in December, 1835 was one of the earliest examples. Other examples were exported to the Netherlands, Russia and Italy. By 1838 the 2-2-2 had become the standard passenger design by Robert Stephenson & Company.

Eighteen of the first nineteen locomotives ordered by Isambard Kingdom Brunel for the opening of the Great Western Railway in 1837/8 were of the 2-2-2 type. These included six 2-2-2 locomotives built by Charles Tayleur at his Vulcan Foundry. Also in 1837 the successful North Star broad gauge locomotive was delivered to the Great Western Railway by Stephenson, becoming the first of a class of twelve locomotives by 1841.

Sharp, Roberts & Company constructed more than 600 2-2-2 locomotives between 1837 and 1857. Ten of these supplied to the Grand Junction Railway became the basis of Alexander Allan's successful designs for the railway from 1845 (the first of which, formerly named Columbine, is preserved). John Rennie supplied 2-2-2 locomotives to the London and Croydon Railway from 1838 and the London and Brighton Railway in 1840. Arend ("eagle") was one of the two first steam locomotives in the Netherlands, built by R. B. Longridge and Company of Bedlington, Northumberland in 1839.

The Great Western Railway continued to order both broad gauge and standard gauge locomotives on the railway, including the Firefly and Sun classes (1840–42), which were enlarged versions of North Star. Bury, Curtis and Kennedy supplied six 2-2-2 locomotives to the Bristol and Gloucester Railway in 1844, and fourteen to the Great Southern and Western Railway in Ireland in 1848, (the last of these has been preserved at Cork Kent railway station.

The Jenny Lind locomotive, designed by David Joy and built in 1847 for the London, Brighton and South Coast Railway by the E. B. Wilson and Company of Leeds, became the basis of hundreds of similar passenger locomotives built during the 1840s and 1850s by this and other manufacturers for UK railways. The London and North Western Railway Cornwall locomotive was designed at Crewe Works as a 4-2-2 by Francis Trevithick in 1847, but was rebuilt as a 2-2-2 in 1858.

Although by the 1860s the 2-2-2 configuration was beginning to be superseded by the 2-4-0 type with better adhesion, the invention of steam sanding gave 2-2-2 singles a new lease of life, and they continued to be built until the 1890s. Notable late examples include William Stroudley's singles of 1874–1880, William Dean's 157 class of 1878–79, and his 3001 class (1891–92), both for the Great Western Railway. James Holden of the Great Eastern Railway created some 2-2-2 singles in 1889 by removing the coupling rod from a 2-4-0.