Melbourne's tram classification system is based on classes originally devised by the Melbourne & Metropolitan Tramways Board (M&MTB).
[1] At first this was largely based on the order in which the original tramway operators had introduced each different type of tramcar between 1906 and 1920.
[1] Individual tram fleets had been numbered (from 1 upwards) by each of the pre-M&MTB tramway operators, but by 1924 the M&MTB had consolidated the numbering across the combined fleet.
[1] With the introduction of Z class trams, the M&MTB started a new numbering system.
[1] Tramways in Ballarat, Bendigo, Geelong, Sorrento and the Victorian Railways had their own tram numbering systems.