Trolza , formerly known as the Uritsky factory or simply Uritsky, is a trolleybus manufacturer in Russia, located in Engels, Saratov oblast. In the Soviet era it was known as ZiU (, Zavod imeni Uritskogo, plant named after Moisei Uritskiy) or Uritsky factory. The enterprise was founded in Imperial Russia in 1868, but it began producing trolleybuses in 1951.
For many years until at least the early 1990s, ZiU was the world's largest manufacturer of trolleybuses. Around 1996, it was renamed Trolza, short for AO Trolleybusnyi Zavod (Trolleybus Factory).
ZiU/Trolza has built over 65,000 trolleybuses and continues this business now. Historically, the most numerous models of ZiU production were the MTB-82, the ZiU-5, both now discontinued, and the ZiU-9 (latterly known as the ZiU-682). All of them were exported to different countries of the world, including Argentina, Bulgaria, Greece, Mongolia, Hungary, Serbiaetc.
In the 1980s, ZiU was building more than 2,000 trolleybuses per year, mostly for domestic use (in the then Soviet Union) but up to 160 per year for export outside the USSR.