Nesebar (often transcribed as Nessebar and sometimes as Nesebur, Bulgarian: Несебър, pronounced [nɛˈsɛbɐr], Thracian: Melsambria, Greek: Μεσημβρία, Mesembria) is an ancient town 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.

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. The ancient part of the town is situated on a peninsula (previously an island) connected to the mainland by a narrow man-made isthmus, and it bears evidence of occupation by a variety of different civilisations over the course of its existence. Its abundance of historic buildings prompted UNESCO to include Nesebar in its list of World Heritage Sites in 1983.