Cygnus is a northern constellation lying on the plane of the Milky Way, deriving its name from the Latinized Greek word for swan. The swan is one of the most recognizable constellations of the northern summer and autumn, and it features a prominent asterism known as the Northern Cross (in contrast to the Southern Cross). Cygnus was among the 48 constellations listed by the 2nd century astronomer Ptolemy, and it remains one of the 88 modern constellations.

Cygnus contains Deneb, one of the brightest stars in the night sky and one corner of the Summer Triangle, as well as some notable X-ray sources and the giant stellar association of Cygnus OB2. Cygnus is also known as the Northern Cross. Deneb is the tail star in the constellation and is the Arabic word for tail. One of the stars of this association, NML Cygni, is one of the largest stars currently known. The constellation is also home to Cygnus X-1, a distant X-ray binary containing a supergiant and unseen massive companion that was the first object widely held to be a black hole. Many star systems in Cygnus have known planets as a result of the Kepler Mission observing one patch of the sky, an area around Cygnus. In addition, most of the eastern part of Cygnus is dominated by the Hercules–Corona Borealis Great Wall, a giant galaxy filament that is the largest known structure in the observable universe, covering most of the northern sky.

Cygnus is a prominent constellation in the northern sky. Its name means “the swan” in Latin, and it is also known as the Swan constellation.

Cygnus is associated with the myth of Zeus and Leda in Greek mythology. The constellation is easy to find in the sky as it features a well-known asterism known as the Northern Cross. Cygnus was first catalogued the by Greek astronomer Ptolemy in the 2nd century.

Notable objects in the constellation include Cygnus X-1, a famous x-ray source, the bright stars Deneb and Albireo, the Fireworks Galaxy (NGC 6946), and several well-known nebulae: the Pelican Nebula (IC 5070), the North America Nebula (NGC 7000), the Crescent Nebula (NGC 6888), and the Veil Nebula (NGC 6960, 6962, 6979, 6992, and 6995).

Cygnus is the 16th largest constellation in the night sky, occupying an area of 804 square degrees. It lies in the fourth quadrant of the northern hemisphere (NQ4) and can be seen at latitudes between +90° and -40°. The neighboring constellations are Cepheus, Draco, Lacerta, Lyra, Pegasus, and Vulpecula.

Cygnus belongs to the Hercules family of constellations, along with Aquila, Ara, Centaurus, Corona Australis, Corvus, Crater, Crux, Hercules, Hydra, Lupus, Lyra, Ophiuchus, Sagitta, Scutum, Sextans, Serpens, Triangulum Australe, and Vulpecula.

Cygnus has 10 stars with known planets and contains two Messier objects: Messier 29 (NGC 6913) and Messier 39 (NGC 7092). The brightest star in the constellation is Deneb, Alpha Cygni, which is also the 19th brightest star in the sky, with an apparent magnitude of 1.25. There are two meteor showers associated with the constellation: the October Cygnids and the Kappa Cygnids.