Under the Whyte notation for the classification of steam locomotives, 2-4-0 represents the wheel arrangement of two leading wheels on one axle, four powered and coupled driving wheels on two axles, and no trailing wheels.
 Alternative notation
Other equivalent classifications are:
- UIC classification: 1'B (also known as German classification and Italian classification)
- French classification: 120
- Turkish classification: 23
- Swiss classification: 2/3
- Russian classification: 1-2-0
 UK usage
The type was used on the Liverpool and Manchester Railway, the Birmingham and Gloucester Railway, the North Midland Railway and the London and South Western Railway (LSWR) before 1846. One of the earliest examples was the broad-gauge GWR Leo Class, designed by Daniel Gooch and built by R and W Hawthorn and Company, Fenton, Murray and Jackson, and Rothwell and Company during 1841 and 1842.
During 1846-7 Alexander Allan of the newly created London and North Western Railway (LNWR) created the 'Crewe type' of locomotive, with 2-2-2 for passenger classes and 2-4-0 for freight. These designs were widely copied by other railways both in the UK and overseas during the 1850s and 1860s. Between 1846 and 1880 the 2-4-0 was the standard type for passenger and mixed traffic locomotives and was built in large numbers by among others, the LNWR (1846–96), the Midland Railway (1846–1880), the North Eastern Railway (1856–88), the Great Eastern Railway (1856–1902), the Great Northern Railway (1849–97).
During the mid-1840s Sir John Hawkshaw developed a new style of 2-4-0 passenger locomotive with outside cylinders in front of the leading wheels and the rear driving axle behind the firebox (steam engine). This layout provided running steady at high speeds, despite a long overhang at the front. Joseph Beattie of the London and South Western Railway was one of the first British locomotive engineers to use this type on express locomotives. Thus from 1858 he began experimenting with 2-4-0 designs for passenger work, culminating in his 'Seven-Foot' 2-4-0 express passenger locomotives built between 1859-1868. Beattie was also responsible for the long-lived 0298 Class of 2-4-0 well tanks designed for suburban passenger work in 1874, some examples of which were still working in 1961.
Most UK railways used 2-4-0s, including those designed by James Holden on the Great Eastern Railway, Matthew Kirtley on the Midland Railway, Joseph Armstrong on the Great Western Railway and Francis Webb on the London and North Western Railway – one of the latter's types, the Precedent (or Jumbo) class Hardwicke famously set outstanding records for the LNWR during the "Race to the North" in 1895.
 Rest of World
||This section needs additional citations for verification. (July 2011)|
After 1854, the 'Hawkshaw type' of 2-4-0 was adopted by Beyer, Peacock and Company who built many examples of the type for export including to the Swedish State Railways (Statens Järnvägar) in 1856, and the Zealand Railway Denmark in 1870. The Friedrich-Franz Railway, Grand Dutchy of Mecklenburg Switzerland bought 19 'Hawkshaw style' 2-4-0 locomotives from Richard Hartmann in Chemnitz from 1864-1869.
Bavarian B V and Bavarian B VI 2-4-0 locomotives of the Royal Bavarian State Railways (Königlich Bayerische Staats-Eisenbahnen) were the first types to be produced in Bavaria in large numbers (208 in all between 1853 and 1863). One example is preserved in the Nuremberg Transport Museum. Between 1877 and 1885, 294 passenger locomotives of the Prussian P 2 class were delivered to Prussian State Railways and its forebears.
In New Zealand 2 classes of Tank locomotive were built with the 2-4-0T wheel arrangement. They were the NZR D class  and the NZR L class , both classes were designed for mixed traffic use. 5 D locos were built by Dubs and Company in Glasgow Scotland, 19 were built by Neilson and Company and 11 were built by Scott Brothers Ltd of Christchurch. All ten L locos were built by the Avonside Engine Company in Bristol. The first members of the D class entered service in 1874, and all had left the service of NZR by the end of 1927, which allowed the D classification to be used again in 1929. Out of the 33 D locomotives that were built, 7 have been preserved although only D 16 and D 140 are in operational condition. The first L built entered service in 1878 and another 9 Ls were ordered. Out of the 10 Ls built, 3 have survived long enough to be preserved [207 , 208  and 219  and all 3 are operational. In 1893-94, three of the 'L' class 2-4-0 T locomotives were rebuilt at Newmarket workshops with a larger boiler and enlarged cylinders to a 4-4-0 side tank arrangement. This new design was classified 'La' but again the limited coal bunker became a liability. The answer was to provide a larger coal bunker and a trailing pony truck giving them a 4-4-2 T wheel arrangement, and a further four 'L' class were converted. Three were not rebuilt but sold to the PWD in 1901-1903. Three new 4-4-2 T locomotives were built in 1902-1903 and when the conversion program had been completed in 1903, the classification, for all ten locomotives, was changed back to 'L'.
In the collection of the California State Railroad Museum is the J.W. Bowker locomotive, a 2-4-0 engine built by Baldwin Locomotive Works in 1875 for the Virginia & Truckee Railroad. Today, the J.W. Bowker is the sole remaining Baldwin 2-4-0 in existence.
 Usage in fiction
|This section does not cite any references or sources. (June 2011)|
- One of Disney's cartoon characters who was used in the movie Dumbo, Casey Junior, is a little 2-4-0 tender locomotive.
- In the Bugs Bunny cartoon, Hare Trigger, it showed two 2-4-0 tender locomotives passing a telephone pole repeating, Bread and butter.
- Bertram Baxter, British Locomotive Catalogue 1825-1923, Vol.1. Moorland Publishing, 1977. ISBN 0-903485-50-8.
- Hamilton Ellis, Some Classic Locomotives, George Allen and Unwin, 1949, pp.19-32.
- Hamilton Ellis, Pictorial encyclopaedia of railways, Hamlyn, 1968, pp.53-4.
- D.L. Bradley, Locomotives of the London and South Western Railway, Part 1. Railway Correspondence and Travel Society, 1965, p.58.
- Bradley (1965), pp.52-76.
- Hamilton Ellis, Pictorial enclyclopaedia of railways, p.54.
|Wikimedia Commons has media related to: 2-4-0 locomotives|