A complication in watchmaking refers to any feature in a mechanical watch beyond the simple display of hours, minutes, and seconds. Complications are additional functions that enhance the utility and complexity of a timepiece, showcasing the watchmaker's craftsmanship and technical prowess. Common complications include the date display, chronograph, moon phase, perpetual calendar, and tourbillon. Each complication requires intricate engineering and precise assembly, often involving hundreds of tiny components working in harmony.

The date display is one of the simplest complications, showing the current date on the watch face. A chronograph allows the wearer to use the watch as a stopwatch, featuring additional sub-dials for measuring elapsed time. The moon phase complication visually represents the current phase of the moon, adding an aesthetic and functional element. A perpetual calendar automatically adjusts for varying month lengths and leap years, maintaining accurate date information without manual correction. The tourbillon, one of the most prestigious complications, counteracts the effects of gravity on the watch's accuracy by mounting the escapement and balance wheel in a rotating cage.

Complications not only enhance the functionality of a watch but also significantly increase its value and desirability among collectors and enthusiasts.