The prehistoric origins of the Thracians remain obscure, in absence of written historical records. Evidence of Proto-Thracians in the prehistoric period depends on remains of material culture. It is generally proposed that a Proto-Thracian people developed from a mixture of indigenous peoples and Indo-Europeans from the time of Proto-Indo-European expansion in the Early Bronze Age.
In the 6th century some Thracian tribes south of the Danube river made contacts with the invading Slavs and were later Slavicised. Thus they became one of the main ethnic elements in the consolidation of the Bulgarian nation in 8-9th century. Linguistic evidence about this is the presence of Thracian and direct Latin loanwords in Old Bulgarian and modern Bulgarian language.

The archaeological research of the Thracian culture started in the 20th century and especially after World War II, mainly on the territory of Southern Bulgaria. As a result of intensive excavation works in the 1960s and 1970s a number of Thracian tombs and sanctuaries were discovered. More significant among them are: the Tomb of Sveshtari, the Tomb of Kazanlak, Tatul, Seuthopolis, Perperikon, the Tomb of Aleksandrovo, Sarmizegetusa, etc.

Also a large number of elaborately crafted gold and silver treasure sets from the 5th and 4th century BC were unearthed. In the following decades those were exposed in museums around the world, thus gaining popularity and becoming an emblem of the ancient Thracian culture. Since the year 2000, Bulgarian archaeologist Georgi Kitov has made discoveries in Central Bulgaria which were summarized as "The Valley of the Thracian Kings".