The aim of the presented paper is to introduce the reader to hardware-in-the-loop (HIL) simulation in electric drives, the motivation for its usage and its benefits. Basic information about HIL simulation in general and the connection to electric drives is followed by an explanation of the main principle of the dynamic emulation of mechanical loads for electric drives, which is a special case of HIL simulation. Next, the description of the three main methods of load emulation and their mathematical background are presented in the order of historical appearance: the emulation with compensator and tracking controller, the emulation based on non-linear control and the emulation with feed-forward compensation with the use of inverse dynamics.