同步辐射是带电粒子的运动速度接近光速（v≈c）在电磁场中偏转时，沿运动的切线方向发出的一种电磁辐射，最先在电子同步加速器上发现，故得此名，又称同步加速器辐射。它与回旋辐射（由回旋加速器产生的辐射）类似，区别是同步辐射中的电子速度更高，已接近光速，要考虑相对论效应。

由于重子的静止质量比电子大三个数量级以上，即使在TeV级的质子同步加速器中，因同步辐射造成的能量损失依然是不重要的。而对MeV级的电子同步加速器，同步辐射已十分显着。同步辐射使粒子在横向和纵向的振荡阻尼，并与量子起伏达到平衡态。这也是为什幺电子同步加速器中束流易于稳定和束流发射度较小且不依赖于入射束性能的原因。

The electromagnetic radiation emitted when charged particles are accelerated radially (a ⊥ v) is called synchrotron radiation. It is produced, for example, in synchrotrons using bending magnets, undulators and/or wigglers. It is similar to cyclotron radiation except that synchrotron radiation is generated by the acceleration of ultrarelativistic charged particles through magnetic fields. Synchrotron radiation may be achieved artificially in synchrotrons or storage rings, or naturally by fast electrons moving through magnetic fields. The radiation produced in this way has a characteristic polarization and the frequencies generated can range over the entire electromagnetic spectrum.