同步带，也称齿形带、正时带、无滑差带等。与常见的普通V带、平带等带传动方式相似，同步带是一种挠性传动形式。

V带、平带等传统带传动方式完全依赖摩擦力传递力，其不可避免的有相对滑动，会导致其实际减速比高于理论减速比，且会随载荷变化而变化，无法精确的传导运动。与之不同，同步带的工作面具有齿形，与带轮的齿槽作啮合传动，并由带的抗拉层承受负载以保持其节线长度不变，故带与带轮间没有相对滑动，主、从动轮间可以保持同步传动。由于其主要依赖齿面正压力传递力，故其带轮尺寸、中心距可以减小，速比可达10，传动效率可达99.5%，带速可达50m/s。

A timing belt, timing chain or cam belt is a part of an internal combustion engine that synchronizes the rotation of the crankshaft and the camshaft(s) so that the engine's valves open and close at the proper times during each cylinder's intake and exhaust strokes. In an interference engine the timing belt or chain is also critical to preventing the piston from striking the valves. A timing belt is usually a toothed belt -- a drive belt with teeth on the inside surface. A timing chain is a roller chain.