In rail transport a wheel arrangement is a system of classifying the arrangement of the wheel assemblies of a locomotive by type, position, and connections. There are serveral notations used to describe wheel arrangements, the use of which varies by country. Within a given country different notations may be employed for different kinds of locomotives, such as steam, electric, and diesel.

In the United States, the United Kingdom and Ireland, the Whyte notation is generally used for steam locomotives. British practice uses a slightly simplified form of the UIC notation for diesels and electrics. The United States uses the AAR wheel arrangement scheme for diesels and electrics.

In mainland Europe, the UIC classification scheme is generally used, with some exceptions. In France, the UIC classification is used for diesels and electrics while a scheme similar to the Whyte notation, but counting axles insteads of wheels, is used for steam locomotives.

Especially in steam days, wheel arrangement was an important attribute of a locomotive, because there were many different ones, each optimised for a different use. Modern diesel and electric locomotives are much more uniform, usually with all axles driven.

Major Notation Schemes

• AAR wheel arrangement - Used largely throughout the US and Canada.
• UIC classification - Used for diesel and electric locomotives in the UK. Used in mainland Europe for all locomotive types, including steam.
• Whyte notation - Used for shunting locomotives and steam locomotives in the UK.