Interlocking in railway terminology (US) is a term used to describe an at-grade crossing or other junction of two or more railroads, or any railroad switching complex in which the switches and the signals controlling train movement over those switches is interlocked so that it is impossible to give clear signals to opposing trains in such a way that the trains would collide.

An interlocking also makes it impossible to give a clear signal to a train if the switches are not aligned properly so that the train movement can be accomplished.

Interlocking was, and often still is, accomplished by mechanical means, in which the levers and mechanism controlling the switches and signals can not be physically placed in conflict. More modern plants may be controlled by electronic circuitry.

In music, the term interlocking is occasionally used to describe a Hocket.