π键，在化学上是共价键的一种。当两个电子轨道的突出部分发生重叠时产生。

名字中的希腊字母π代表了p轨域，因为π键的轨道对称性与p轨域相同。p轨域通常参与形成π键，然而，d轨域同样能参与形成。

π键通常比σ键弱，因为它的电子云距离带正电的原子核的距离更远，需要更多的能量。量子力学的观点认为，键的强度很弱主要是因为平行的p轨域间重叠不足。

In chemistry, pi bonds (π bonds) are covalent chemical bonds where two lobes of one involved atomic orbital overlap two lobes of the other involved atomic orbital. Each of these atomic orbitals is zero at a shared nodal plane, passing through the two bonded nuclei. The same plane is also a nodal plane for the molecular orbital of the pi bond.