Brandenburg (German: [ˈbʁandn̩bʊʁk] (listen); Low German: Brannenborg; Lower Sorbian: Bramborska [ˈbrambɔrska]) is a state in the northeast of Germany bordering the states of Mecklenburg-Vorpommern, Lower Saxony, Saxony-Anhalt, and Saxony, as well as the country of Poland. With an area of 29,480 square kilometres (11,380 sq mi) and a population of 2.5 million residents, it is the fifth-largest German state by area and the tenth-most populous. Potsdam is the state capital and largest city, and other major towns are Cottbus, Brandenburg an der Havel and Frankfurt (Oder).

Brandenburg surrounds the national capital and city-state of Berlin, and together they form the Berlin/Brandenburg Metropolitan Region, the third-largest metropolitan area in Germany with a total population of about 6.2 million. There was an unsuccessful attempt to unify both states in 1996 and the states cooperate on many matters to this day.

Brandenburg originated in the Northern March in the 900s AD, from areas conquered from the Wends. It later became the Margraviate of Brandenburg, a major principality of the Holy Roman Empire. In the 15th century, it came under the rule of the House of Hohenzollern, which later also became the ruling house of the Duchy of Prussia and established Brandenburg-Prussia, the core of the later Kingdom of Prussia. From 1815 to 1947, Brandenburg was a province of Prussia.

Following the abolition of Prussia after World War II, Brandenburg was established as a state by the Soviet Military Administration in Germany, and became a state of the German Democratic Republic in 1949. In 1952, the state was dissolved and broken up into multiple regional districts. Following German reunification, Brandenburg was re-established in 1990 and became one of the five new states of the Federal Republic of Germany.

The Prince-Bishopric of Brandenburg (German: Hochstift Brandenburg) was an ecclesiastical principality of the Holy Roman Empire from the 12th century until it was secularized during the second half of the 16th century. It should not be confused with the larger Diocese of Brandenburg (Latin: Dioecesis Brandenburgensis) established by King Otto I of Germany in 948, in the territory of the Marca Geronis (Saxon Eastern March) east of the Elbe river. The diocese, over which the prince-bishop exercised only spiritual authority, was a suffragan diocese of the Archdiocese of Magdeburg, its seat was Brandenburg an der Havel.

The Prince-Bishopric of Brandenburg was an imperial estate of the Holy Roman Empire for some time, probably starting about 1161/1165. However, the Brandenburg bishops never managed to gain control over a significant territory, being overshadowed by the Margraviate of Brandenburg, which was originally seated in the same city. Chapter and cathedral, surrounded by further ecclesiastical institutions, were located on the Dominsel (Cathedral Island), which formed a prince-episcopal cathedral immunity district (Domfreiheit), distinct from the city of Brandenburg. Only in 1929 the - meanwhile former - immunity district was incorporated into the city itself.