在物理学里，哈密顿原理(Hamilton's principle)是爱尔兰物理学家威廉·哈密顿于1833年发表的关于平稳作用量原理的表述。哈密顿原理阐明，一个物理系统的拉格朗日函数，所构成的泛函的变分问题解答，可以表达这物理系统的动力行为。拉格朗日函数又称为拉格朗日量，包含了这物理系统所有的物理内涵。这泛函称为作用量。哈密顿原理提供了一种新的方法来表述物理系统的运动。不同于牛顿运动定律的微分方程序方法，这方法以积分方程序来设置系统的作用量，在作用量平稳的要求下，使用变分法来计算整个系统的运动方程序。

In physics, Hamilton's principle is William Rowan Hamilton's formulation of the principle of stationary action (see that article for historical formulations). It states that the dynamics of a physical system is determined by a variational problem for a functional based on a single function, the Lagrangian, which contains all physical information concerning the system and the forces acting on it. The variational problem is equivalent to and allows for the derivation of the differential equations of motion of the physical system. Although formulated originally for classical mechanics, Hamilton's principle also applies to classical fields such as the electromagnetic and gravitational fields, and has even been extended to quantum mechanics, quantum field theory and criticality theories.