Nesebar is an ancient city and one of the major seaside resorts on the Bulgarian Black Sea Coast, located in Burgas Province. It is the administrative centre of the homonymous Nesebar Municipality. Often referred to as the "Pearl of the Black Sea", Nesebar is a rich city-museum defined by more than three millennia of ever-changing history. The small city exists in two parts separated by a narrow man-made isthmus with the ancient part of the settlement on the peninsula (previously an island), and the more modern section (i.e. hotels, later development) on the mainland side. The older part bears evidence of occupation by a variety of different civilisations over the course of its existence.

It is one of the most prominent tourist destinations and seaports on the Black Sea, in what has become a popular area with several large resorts—the largest, Sunny Beach, is situated immediately to the north of Nesebar.

Nesebar has on several occasions found itself on the frontier of a threatened empire, and as such it is a town with a rich history. Due to the city's abundance of historic buildings, UNESCO came to include Nesebar in its list of World Heritage Sites in 1983.

As of December 2019, the town has a population of 13,600 inhabitants.

The settlement was known in Greek as Mesembria, sometimes mentioned as Mesambria or Melsembria, the latter meaning the city of Melsas. According to a reconstruction the name might derive from Thracian Melsambria. Nevertheless, the Thracian origin of that name seems to be doubtful. Moreover, the tradition pertaining to Melsas, as founder of the city is tenuous and belongs to a cycle of etymological legends abundant among Greek cities. It also appears that the story of Melsas was a latter reconstruction of the Hellenistic era, when Mesembria was an important coastal city.

Before 1934, the common Bulgarian name for the town was Mesemvriya. It was replaced with the current name, which was previously used in the Erkech dialect spoken close to Nesebar. Both forms are derived from the Greek Mesembria.