Barnard's Star is a red dwarf about six light-years from Earth in the constellation of Ophiuchus. It is the fourth-nearest-known individual star to the Sun after the three components of the Alpha Centauri system, and the closest star in the northern celestial hemisphere. Its stellar mass is about 14% of the Sun's. Despite its proximity, the star has a dim apparent magnitude of +9.5 and is invisible to the unaided eye; it is much brighter in the infrared than in visible light.

The star is named after the American astronomer E. E. Barnard, who in 1916 measured its proper motion as 10.3 arcseconds per year relative to the Sun, the highest known for any star. The star had previously appeared on Harvard University photographic plates in 1888 and 1890.

Barnard's Star is among the most studied red dwarfs because of its proximity and favorable location for observation near the celestial equator. Historically, research on Barnard's Star has focused on measuring its stellar characteristics, its astrometry, and also refining the limits of possible extrasolar planets. Although Barnard's Star is ancient, it still experiences star flare events, one being observed in 1998.

From the early 1960s to the early 1970s, Peter van de Kamp argued that planets orbited Barnard's star. His specific claims of large gas giants were refuted in the mid-1970s after much debate.

In November 2018, a candidate super-Earth planetary companion known as Barnard's Star b was reported to orbit Barnard's Star. It was believed to have a minimum of 3.2 M_Earth (Earth masses) and orbit at 0.4 AU. However, work presented in July 2021 cast doubts upon the existence of this planet.