在量子力学里，泡利不相容原理（Pauli exclusion principle）表明，两个全同的费米子不能处于相同的量子态。这原理是由沃尔夫冈·泡利于1925年通过分析实验结果得到的结论。例如，由于电子是费米子，在一个原子里，每个电子都拥有独特的一组量子数，两个电子各自拥有的一组量子数不能完全相同，假若它们的主量子数，角量子数，磁量子数分别相同，则自旋磁量子数必定不同，它们必定拥有相反的自旋磁量子数。换句话说，处于同一原子轨道的两个电子必定拥有相反的自旋方向。泡利不相容原理简称为泡利原理或不兼容原理。

The Pauli exclusion principle is the quantum mechanical principle that states that two identical fermions (particles with half-integer spin) cannot occupy the same quantum state simultaneously. In the case of electrons, it can be stated as follows: it is impossible for two electrons of a poly-electron atom to have the same values of the four quantum numbers: n, the principal quantum number, ℓ, the angular momentum quantum number, m_ℓ, the magnetic quantum number, and m_s, the spin quantum number. For two electrons residing in the same orbital, n, ℓ, and m_ℓ are the same, so m_s, the spin, must be different, and thus the electrons have opposite half-integer spins, 1/2 and -1/2. This principle was formulated by Austrian physicist Wolfgang Pauli in 1925.