波函数塌缩指的是某些量子力学体系与外界发生某些作用后波函数发生突变，变为其中一个本征态或有限个具有相同本征值的本征态的线性组合的现象。波函数塌缩可以用来解释为何在单次测量中被测定的物理量的值是确定的（虽然多次测量中每次测量值可能都不同）。

在某一些量子物理理论中，波函数的塌缩是量子系统遵守量子物理定律的两种方法之一。波函数坍塌的真实性并没有被完全地确定；科学家一直在争论，波函数塌缩是这个世界的自然现象之一，还是仅是属于某个现象的一部份，比如量子脱散的附属现象。近年来，量子脱散已取代波函数坍塌为更受量子物理学家欢迎的理论。

In quantum mechanics, wave function collapse is said to occur when a wave function—initially in a superposition of several eigenstates—appears to reduce to a single eigenstate (by "observation"). It is the essence of measurement in quantum mechanics and connects the wave function with classical observables like position and momentum. Collapse is one of two processes by which quantum systems evolve in time; the other is continuous evolution via the Schrödinger equation. However, in this role, collapse is merely a black box for thermodynamically irreversible interaction with a classical environment. Calculations of quantum decoherence predict apparent wave function collapse when a superposition forms between the quantum system's states and the environment's states. Significantly, the combined wave function of the system and environment continue to obey the Schrödinger equation.