潮汐力或引潮力是万有引力的效果，它使得潮汐发生。它源于在一个星体的直径上各点的引力场不相等。

当一个天体甲受到天体乙的引力的影响，力场在甲面对乙跟背向乙的表面的作用，有很大差异。这使得甲出现很大应变，甚至会化成碎片（参见洛希极限）。除非引力场完全相等，否则这些应变还是会出现。

潮汐力会改变天体的形状而不改变其体积。地球的每部分都受到月球的引力影响而加速，在地球的观察者因此看到海洋内的水不断重新分布。

当天体受潮汐力而自转，内部摩擦力会令其旋转动能化为内能，内能继而转成热。若天体相当接近系统内质量最大的天体，自转的天体便会以同一面朝质量最大的天体公转，即潮汐锁定，例如月球和地球。

The tidal force is a secondary effect of the force of gravity and is responsible for the tides. It arises because the gravitational force exerted by one body on another is not constant across it; the nearest side is attracted more strongly than the farthest side. Thus, the tidal force is differential. Consider the gravitational attraction of the moon on the oceans nearest to the moon, the solid Earth and the oceans farthest from the moon. There is a mutual attraction between the moon and the solid earth which can be considered to act on its centre of mass. However, the near oceans are more strongly attracted and, since they are fluid, they approach the moon slightly, causing a high tide. The far oceans are attracted less. The attraction on the far-side oceans could be expected to cause a low tide but since the solid earth is attracted (accelerated) more strongly towards the moon, there is a relative acceleration of those waters in the outwards direction. Viewing the Earth as a whole, we see that all its mass experiences a mutual attraction with that of the moon but the near oceans more so than the far oceans, leading to a separation of the two.