进动（precession）是自转物体之自转轴又绕着另一轴旋转的现象，又可称作旋进。在天文学上，又称为「岁差现象」。

常见的例子为陀螺。当其自转轴的轴线不再呈铅直时，即自转轴与对称轴不重合不平行时，会发现自转轴会沿着铅直线作旋转，此即「旋进」现象。另外的例子是地球的自转。

对于量子物体如粒子，其带有自旋特征，常将之模拟于陀螺自转的例子。然而实际上自旋是一个内禀性质，并不是真正的自转。粒子在标准的量子力学处理上是视为点粒子，无法说出一个点是怎样自转。若要将粒子视为带质量球状物体来计算，以电子来说，会发现球表面转速超过光速，违反狭义相对论的说法。

Precession is a change in the orientation of the rotational axis of a rotating body. In an appropriate reference frame it can be defined as a change in the first Euler angle, whereas the third Euler angle defines the rotation itself. In other words, if the axis of rotation of a body is itself rotating about a second axis, that body is said to be precessing about the second axis. A motion in which the second Euler angle changes is called nutation. In physics, there are two types of precession: torque-free and torque-induced.