The common nightingale, rufous nightingale or simply nightingale (Luscinia megarhynchos), is a small passerine bird which is best known for its powerful and beautiful song. An Old World flycatcher, it belongs to a group of more terrestrial species, often called chats. Its range partly overlaps with that of the more northerly thrush nightingale (Luscinia luscinia), a closely related species with which hybrids have occurred.

The common nightingale belongs to a distinctive group of Old World flycatchers, known as chats, that were formerly thought to be thrushes. Genetic analysis showed that they were in fact a type of flycatcher (Muscicapidae), with the resemblance to thrushes being the result of convergent evolution. "Nightingale" is derived from "night" and the Old English galan, "to sing". The genus name Luscinia is Latin for "nightingale" and megarhynchos is from Ancient Greek megas, "great" and rhunkhos, "bill".

Three subspecies are recognized:

The common nightingale is slightly larger than the European robin, at 15–16.5 cm (5.9–6.5 in) length. It is plain brown above except for the reddish tail. It is buff to white below. The sexes are similar. The eastern subspecies (L. m. golzi) and the Caucasian subspecies (L. m. africana) have paler upper parts and a stronger face-pattern, including a pale supercilium. The song of the male nightingale has been described as one of the most beautiful sounds in nature, inspiring songs, fairy tales, opera, books, and a great deal of poetry. However, historically most people were not aware that female nightingales do not sing.

It is a migratory insectivorous species breeding in forest and scrub in Europe and the Palearctic, and wintering in Sub-Saharan Africa. It is not found naturally in the Americas. The distribution is more southerly than the very closely related thrush nightingale (Luscinia luscinia). It nests on or near the ground in dense vegetation. Research in Germany found that favoured breeding habitat of nightingales was defined by a number of geographical factors.

In the U.K., the bird is at the northern limit of its range which has contracted in recent years, placing it on the red list for conservation. Despite local efforts to safeguard its favoured coppice and scrub habitat, numbers fell by 53 percent between 1995 and 2008. A survey conducted by the British Trust for Ornithology in 2012 and 2013 recorded some 3,300 territories, with most of these clustered in a few counties in South East England and East Anglia, notably Kent, Essex, Suffolk, and East and West Sussex.

By contrast, the European breeding population is estimated at between 3.2 and 7 million pairs, giving it green conservation status (least concern).

Nightingales are so named because they frequently sing at night as well as during the day. The name has been used for more than 1,000 years, being highly recognisable even in its Old English form nihtegale, which means "night songstress". Early writers assumed the female sang when it is in fact the male. The song is loud, with an impressive range of whistles, trills and gurgles. The male nightingales can produce a variable number of distinct song types whereas different individual birds can sing the same song type with minor variations (between them, or from rendition to rendition), resulting in extraordinarily large song repertoires (on average 190 with a maximum of 250 different song types). Its song is particularly noticeable at night because few other birds are singing. This is why its name includes "night" in several languages. Only unpaired males sing regularly at night, and nocturnal song probably serves to attract a mate. Singing at dawn, during the hour before sunrise, is assumed to be important in defending the bird's territory. Nightingales sing even more loudly in urban or near-urban environments, in order to overcome the background noise. The most characteristic feature of the song is a loud whistling crescendo that is absent from the song of its close relative, the thrush nightingale (Luscinia luscinia). It has a frog-like alarm call.