Albireo /ælˈbɪrioʊ/ is a double star designated Beta Cygni (β Cygni, abbreviated Beta Cyg, β Cyg). The International Astronomical Union uses the name "Albireo" specifically for the brightest star in the system. Although designated 'beta', it is fainter than Gamma Cygni, Delta Cygni, and Epsilon Cygni and is the fifth-brightest point of light in the constellation of Cygnus. Appearing to the naked eye to be a single star of magnitude 3, viewing through even a low-magnification telescope resolves it into its two components. The brighter yellow star, itself a very close trinary system, makes a striking colour contrast with its fainter blue companion.

β Cygni (Latinised to Beta Cygni) is the system's Bayer designation. The brighter of the two components is designated β¹ Cygni or Beta Cygni A and the fainter β² Cygni or Beta Cygni B.

The origin of the star system's traditional name Albireo is unclear. Christian Ludwig Ideler traced it to the heading for the constellation we call Cygnus in Ptolemy's star catalog, in the translation of the Almagest by Gerard of Cremona: "Stellatio Eurisim: et est volans; et jam vocatur gallina. et dicitur eurisim quasi redolens ut lilium ab ireo" ("Constellation Eurisim: and it is the Flyer, and it is also called the Hen, and it is called Eurisim as if redolent like the lily from the 'ireo'"). (The original Greek just calls the constellation "Ορνιθος αστερισμος", "the constellation of the Bird".) The word "ireo" is obscure as well – Ideler suggests that Gerard took "Eurisim" to mean the plant Erysimum, which is called irio in Latin, but the ablative case of that is not "ireo" but irione. In any case, Ideler proposed that (somehow) the phrase "ab ireo" was applied to the star at the head of the bird, and this became "Albireo" when an "l" was mistakenly inserted as though it was an Arabic name. Ideler also supposed that the name Eurisim was a mistaken transliteration of the Arabic name "Urnis" for Cygnus (from the Greek "Ορνις").

In 2016, the International Astronomical Union (IAU) organized a Working Group on Star Names (WGSN) to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016 included a table of the first two batches of names approved by the WGSN; which included Albireo for β Cygni Aa. It is now so entered in the IAU Catalog of Star Names.

Medieval Arabic-speaking astronomers called Beta Cygni minqār al-dajāja^h (English: the hen's beak). The term minqār al-dajāja^h (منقار الدجاجة) or Menchir al Dedjadjet appeared in the catalogue of stars in the Calendarium of Al Achsasi Al Mouakket, which was translated into Latin as Rostrum Gallinae, meaning the hen's beak.

Since Cygnus is the swan, and Beta Cygni is located at the head of the swan, it is sometimes called the "beak star". With Deneb, Gamma Cygni (Sadr), Delta Cygni, and Epsilon Cygni (Gienah), it forms the asterism called the Northern Cross.

Beta Cygni is about 420 light-years (129 pc) away from the Sun. When viewed with the naked eye, Albireo appears to be a single star. However, in a telescope it resolves into a double star consisting of β Cygni A (amber, apparent magnitude 3.1), and β Cygni B (blue-green, apparent magnitude 5.1). Separated by 35 seconds of arc, the two components provide one of the best contrasting double stars in the sky due to their different colors.

It is not known whether the two components β Cygni A and B are orbiting around each other in a physical binary system, or if they are merely an optical double. If they are a physical binary, their orbital period is probably at least 100,000 years. Some experts, however, support the optical double argument, based on observations that suggest different proper motions for the components, which implies that they are unrelated. The primary and secondary also have different measured distances from the Hipparcos mission – 434 ± 20 light-years (133 ± 6 pc) for the primary and 401 ± 13 light-years (123 ± 4 pc) for the secondary. More recently the Gaia mission has measured distances of about 330–390 light years (100–120 parsecs) for both components, but noise in the astrometric measurements for the stars means that data from Gaia's second data release is not yet sufficient to determine whether the stars are physically associated.