A reticle, or reticule (from Latin reticulum 'net'), also known as a graticule (from Latin craticula 'gridiron'), is a pattern of fine lines or markings built into the eyepiece of a sighting device, such as a telescopic sight in a telescope, a microscope, or the screen of an oscilloscope, to provide measurement references during visual examination. Today, engraved lines or embedded fibers may be replaced by a computer-generated image superimposed on a screen or eyepiece. Both terms may be used to describe any set of lines used for optical measurement, but in modern use reticle is most commonly used for gunsights and such, while graticule is more widely used for the oscilloscope display, microscope slides, and similar roles.

There are many variations of reticles; this article concerns itself mainly with a simple reticle: crosshairs. Crosshairs are most commonly represented as intersecting lines in the shape of a cross, "+", though many variations exist, including dots, posts, circles, scales, chevrons, or a combination of these. Most commonly associated with telescopic sights for aiming firearms, crosshairs are also common in optical instruments used for astronomy and surveying, and are also popular in graphical user interfaces as a precision pointer. The reticle is said to have been invented by Robert Hooke, and dates to the 17th century. Another candidate as inventor is the amateur astronomer William Gascoigne, who predated Hooke.