Birka listen^ⓘ (Birca in medieval sources), on the island of Björkö (lit. "Birch Island") in present-day Sweden, was an important Viking Age trading center which handled goods from Scandinavia as well as many parts of Continental Europe and the Orient. Björkö is located in Lake Mälaren, 30 kilometers west of contemporary Stockholm, in the municipality of Ekerö.

Birka was founded around AD 750 and it flourished for more than 200 years. It was abandoned c. AD 975, around the same time Sigtuna was founded as a Christian town some 35 km to the northeast. It has been estimated that the population in Viking Age Birka was between 500 and 1000 people.

The archaeological sites of Birka and Hovgården, on the neighbouring island of Adelsö, make up an archaeological complex which illustrates the elaborate trading networks of Viking Scandinavia and their influence on the subsequent history of Europe. Generally regarded as Sweden's oldest town, Birka (along with Hovgården) has been a UNESCO World Heritage Site since 1993. Many burial sites have been uncovered at Birka, leading to the finding of many objects including jewelry and many textile fragments. In recent years, objects from Birka have been in the public eye due to ongoing academic research connecting Birka to evidence of trade with the Middle East.

Birka was founded around 750 AD as a trading port by a king or merchants trying to control trade. It is one of the earliest urban settlements in Scandinavia. Birka was the Baltic link in the Dnieper Trade Route through Ladoga (Aldeigja) and Novgorod (Holmsgard) to the Byzantine Empire and the Abbasid Caliphate. Birka is the site of the first known Christian congregation in Sweden, founded in 831 by Saint Ansgar.

As a trading center, Birka most likely offered furs, iron goods, and craft products, in exchange for various materials from much of Europe and Western Asia. Furs were obtained from the Sami people, the Finns, and people in Northwestern Russia, as well as from local trappers. Furs included bear, fox, marten, otter, beaver, and other species. Reindeer antlers and objects carved from reindeer antlers like combs were important items of trade. The trade of walrus tusks, amber, and honey is also documented.

Foreign goods found from the graves of Birka include glass and metalware, pottery from the Rhineland, clothing and textiles including Chinese silk, Byzantine embroidery with extremely fine gold thread, brocades with gold passementerie, and plaited cords of high quality. From the ninth century onwards coins minted at Haithabu in Northern Germany and elsewhere in Scandinavia start to appear. However, the vast majority of the coins found at Birka are silver dirhams from the Middle East while English and Carolingian coins are rare.

Sources from Birka are mainly archaeological remains. No texts survive from this area, though the written text Vita Ansgari ("The Life of Ansgar") by Rimbert (c. 865) describes the missionary work of Ansgar around 830 at Birka, and Gesta Hammaburgensis Ecclesiae Pontificum (Deeds of Bishops of the Hamburg Church) by Adam of Bremen in 1075 describes the Archbishop Unni, who died at Birka in 936. Saint Ansgar's work was the first attempt to convert the people of Birka from the Norse religion to Christianity. It was unsuccessful.

Both Rimbert and Adam were German clergymen writing in Latin. There are no known Norse sources mentioning the name of the settlement, or even the settlement itself, and the original Norse name of Birka is unknown. Birca is the Latinised form given in the written sources by Rimbert and Adam; and Birka is the contemporary, unhistorical Swedish form. The Latin name is probably derived from an Old Norse word "birk" which probably means a market place. Related to this was the Bjärköa law (bjärköarätt) which regulated the life of market places in Denmark, Norway and Sweden. Birka and similar spellings are very common in Scandinavian place names still today leading to speculation that all references to Birka, especially those by Adam of Bremen, were not about the same location.