4-4-0

4-4-0 is a locomotive type with a classification that uses the Whyte notation for the classification of steam locomotives by wheel arrangement and represents the arrangement: four leading wheels on two axles (usually in a leading bogie), four powered and coupled driving wheels on two axles, and a lack of trailing wheels. Due to the large number of the type that were produced and used in the United States, the 4-4-0 is most commonly known as the "American" or "Eight-Wheeler" type, but the type subsequently also became popular in the United Kingdom, where large numbers were produced.

Almost every major railroad that operated in North America in the first half of the 19th century owned and operated locomotives of this type.

The first use of the name American to describe locomotives of this wheel arrangement was made by Railroad Gazette in April 1872. Prior to that, this wheel arrangement was known as a standard or eight-wheeler.

This locomotive type was so successful on railroads in the United States that many earlier 4-2-0 and 2-4-0 locomotives were rebuilt as 4-4-0s by the middle of the 19th century.

Several 4-4-0 tank locomotives were built, but the vast majority of locomotives of this wheel arrangement were tender engines.