Commonwealth Engineering, often shortened to Com-Eng, later known as Comeng [/ˈkɒmɛndʒ/ KOM-enj], was an Australian engineering company that designed and built railway locomotives, rolling stock and trams.

Smith and Waddington, the predecessor to Commonwealth Engineering, was founded in 1921, in the Sydney suburb of Camperdown, as a body builder for custom motor cars.

The government purchased a controlling stake in the company in 1946 and changed the name to Commonwealth Engineering.

The site, which was situated between the Great Western Highway and Main Western railway line west of Duck River, has been replaced with new developments including high-rise housing and light industries.

In 1990, the Dandenong plant was sold to ABB (later Bombardier Transportation, now Alstom), while the Bassendean facility was sold to A Goninan & Co. John Dunn has written a history of Comeng: Leyland OPSU1/1s Media related to Commonwealth Engineering at Wikimedia Commons