Under the Whyte notation for the classification of steam locomotives, 0-2-2-0 represents the wheel arrangement of no leading wheels, four powered but uncoupled driving wheels on two axles, and no trailing wheels.^[1] Some authorities place brackets around the duplicated but uncoupled wheels, creating a notation 0-(2-2)-0.^[2]

The first recorded usage of the arrangement was in the G&SWR 99 Class designed by Patrick Stirling for the Glasgow and South Western Railway in 1855.^[2] The design was not successful and the locomotives were withdrawn by 1867. It would later be used on the Royal Bavarian State Railways ML 2/2 class of 1906, which were much more numerous and successful.

The Mount Washington Cog Railway has eight 0-2-2-0's and only two are in working order, with three in storage and the remainder on display.