Buses are the cornerstone of the Belgrade public transport system, but there is also a number of tram lines, which commonly connect Novi Beograd with the other side of the Sava, and trolleybuses, most of which serve the city center.
The transport system is cheap, with tickets valid for 90 minutes of travel costing less than one euro. If you plan on staying in Belgrade for an extended period of time, you should look into monthly transportation passes. Nighttime bus services run from midnight to 4 am and require purchasing a special ticket on board.
Belgrade’s public transport system also offers a handy app for Android and iOS where you can track the locations of all buses in proximity.