Thrace (/θreɪs/, thrayss; Bulgarian: Тракия, romanised: Trakiya; Greek: Θράκη, romanised: Thráki; Turkish: Trakya) is a geographical and historical region in Southeast Europe roughly corresponding to the province of Thrace in the Roman Empire. Bounded by the Balkan Mountains to the north, the Aegean Sea to the south, and the Black Sea to the east, it comprises present-day southeastern Bulgaria (Northern Thrace), northeastern Greece (Western Thrace), and the European part of Turkey (East Thrace). Lands also inhabited by ancient Thracians extended in the north to modern-day Northern Bulgaria and Romania and to the west into Macedonia.

The word Thrace, from ancient Greek Thrake (Θρᾴκη), referred originally to the Thracians (ancient Greek Thrakes Θρᾷκες), an ancient people inhabiting Southeast Europe. The name Europe (ancient Greek Εὐρώπη), also at first referred to this region, before that term expanded to include its modern sense.

It has been suggested that the name Thrace derives from the name of the principal river of the region, the Hebros. The river's name may be derived from the Indo-European arg "white river" (the opposite of Vardar, meaning "black river"). According to an alternative theory, Hebros means "goat" in Thracian.

Sixth century geographer Stephanus of Byzantium claimed that, long before the ancient Greeks started referring to the region as Thrace, it was known as Aria (Αρια) and Perki (Περκη).

In Turkish, Thrace is commonly referred to as Rumeli, meaning "Land of the Romans", which was the name traditionally given by Turkic societies to the Byzantine Empire and Orthodox Christians.

In Greek mythology, Thrace is named after the heroine and sorceress Thrace, who was the daughter of Oceanus and Parthenope, and sister of Europa.

The historical boundaries of Thrace have varied. The ancient Greeks employed the term "Thrace" to refer to all of the territory which lay north of Thessaly inhabited by the Thracians, a region which "had no definite boundaries" and to which other regions (like Macedonia and even Scythia) were added. In one ancient Greek source, the very Earth is divided into "Asia, Libya, Europa and Thracia". As the Greeks gained knowledge of world geography, "Thrace" came to designate the area bordered by the Danube on the north, by the Euxine Sea (Black Sea) on the east, by northern Macedonia in the south, and by Illyria to the west. This largely coincided with the Thracian Odrysian kingdom, whose borders varied over time. After the Macedonian conquest, this region's former border with Macedonia was shifted from the Struma River to the Mesta River. This usage lasted until the Roman conquest. Henceforth, (classical) Thrace referred only to the tract of land largely covering the same extent of space as the modern geographical region.^{[clarification needed]} In its early period, the Roman province of Thrace was of this extent, but after the administrative reforms of the late 3rd century, Thracia's much reduced territory became the six small provinces which constituted the Diocese of Thrace. The medieval Byzantine theme of Thrace contained only what today is East Thrace.

The largest cities of Thrace are: Istanbul, Plovdiv, Çorlu, Tekirdağ, Burgas, Edirne, Stara Zagora, Sliven, Yambol, Haskovo, Komotini, Alexandroupoli, Xanthi, and Kırklareli.