The lever escapement is the regulating mechanism used in essentially all mechanical wristwatches and most pocket watches manufactured since the late nineteenth century. It transfers energy from the mainspring (via the gear train) to the balance wheel in discrete impulses, and so divides the watch's power flow into the regular oscillations that produce timekeeping. Its dominance is a consequence of an unusually robust trade-off between accuracy, manufacturing tolerance, robustness to shock, and resistance to position-dependent errors.

The mechanism was invented by the English watchmaker Thomas Mudge around 1755, refined progressively by Abraham-Louis Breguet and others in the early nineteenth century, and standardised in its modern form (the "Swiss lever" or "club-tooth lever") by Georges Frederic Roskopf and other Swiss makers in the second half of the nineteenth century. By 1900 it had displaced the cylinder, duplex and verge escapements as the standard for both mid-range and high-grade watches, and it remains so today; even the most prestigious modern complications (perpetual calendars, tourbillons, minute repeaters) typically use a lever escapement at their core, with the tourbillon adding a rotating cage rather than replacing the escapement itself.

The mechanism comprises three principal components: the escape wheel, with characteristic club-shaped teeth; the lever (or pallet fork), pivoted between the escape wheel and the balance, carrying two pallet stones (entry and exit) of synthetic ruby; and the impulse pin (or impulse jewel) on the balance roller, which engages with the lever's notch on each oscillation of the balance. The escape wheel advances by one tooth on each oscillation, the lever rocks back and forth between two banking pins, and a small impulse is delivered to the balance on each rock. The result is a regular tick-tock at the watch's beat rate, typically 18,000, 21,600, 25,200, 28,800 or 36,000 vibrations per hour.

The lever escapement's persistence is partly a matter of inherent merit (its self-starting behaviour, its tolerance to manufacturing variation, its insensitivity to position) and partly a matter of accumulated industrial investment in tooling, training and component supply chains. Higher-performing escapements (the detent, the co-axial designed by George Daniels and used by Omega, the natural escapement of Breguet) exist and are used in specific applications, but none has displaced the lever from its dominant position in production-grade mechanical watchmaking.