在经典力学里，作用量-角度坐标（action-angle coordinate）是一组正则坐标，通常在解析可积分系统 (Integrable system) 时，有很大的用处。应用作用量-角度坐标的方法，不需要先解析运动方程序，就能够求得振动或旋转的频率。作用量-角度坐标主要用于完全可分的 哈密顿-亚可比方程序（哈密顿量显性地不含时间，也就是说，能量保持恒定）。作用量-角度变量可以用来定义一个环面不变量。因为，保持作用量的不变设置了环的曲面，而角度是环面的另外一个坐标，粒子依照着角度，卷绕于环面。

In classical mechanics, action-angle coordinates are a set of canonical coordinates useful in solving many integrable systems. The method of action-angles is useful for obtaining the frequencies of oscillatory or rotational motion without solving the equations of motion. Action-angle coordinates are chiefly used when the Hamilton–Jacobi equations are completely separable. (Hence, the Hamiltonian does not depend explicitly on time, i.e., the energy is conserved.) Action-angle variables define an invariant torus, so called because holding the action constant defines the surface of a torus, while the angle variables parameterize the coordinates on the torus.