Planetary gears are at the heart of modern engineering and are used in gearboxes that power everything from basic plant machinery to cutting-edge electric vehicles. The simple configuration of a central drive and orbiting gears was developed thousands of years ago to model the movements of the planets. Today, engineers use planetary gears in applications that demand high torque density, operational efficiency and durability. In this article, we explore the principles of operation, how planetary gears work, and where you might find them.