The Margraviate of Brandenburg (German: Markgrafschaft Brandenburg) was a major principality of the Holy Roman Empire from 1157 to 1806 that, having electoral status although being quite poor, grew rapidly in importance after inheriting the Duchy of Prussia in 1618 and then came to play a pivotal role in the history of Germany and that of Central Europe as core of the Prussian kingdom.

Brandenburg developed out of the Northern March founded in the territory of the Slavic Wends. It derived one of its names from this inheritance, the March of Brandenburg (Mark Brandenburg). Its ruling margraves were established as prestigious prince-electors in the Golden Bull of 1356, allowing them to vote in the election of the Holy Roman Emperor. The state thus became additionally known as Electoral Brandenburg or the Electorate of Brandenburg (Kurbrandenburg or Kurfürstentum Brandenburg).

The House of Hohenzollern came to the throne of Brandenburg in 1415. In 1417, Frederick I moved its capital from Brandenburg an der Havel to Berlin. By 1535, the electorate had an area of some 10,000 square miles (26,000 km²) and a population of 400,000. Under Hohenzollern leadership, Brandenburg grew rapidly in power during the 17th century and inherited the Duchy of Prussia. The resulting Brandenburg-Prussia was the predecessor of the Kingdom of Prussia, which became a leading German state during the 18th century. Although the electors' highest title was "King in/of Prussia", their power base remained in Brandenburg and its capital Berlin.

The Margraviate of Brandenburg ended with the dissolution of the Holy Roman Empire in 1806. It was replaced after the Napoleonic Wars with the Prussian Province of Brandenburg in 1815. The Hohenzollern Kingdom of Prussia was the primary driving force behind the unification of Germany. The Prussian-dominated North German Confederation later transformed in 1871 into the German Empire; it was the legal predecessor of the united German Reich of 1871–1945, and as such a direct ancestor of the present-day Federal Republic of Germany,

The territory of the former margraviate, commonly known as the Mark Brandenburg,^{[citation needed]} lies in present-day eastern Germany and western Poland. Geographically it encompassed the majority of the present-day German states of Brandenburg and Berlin, the Altmark (the northern third of Saxony-Anhalt), and the Neumark (now divided between Poland's Lubusz and West Pomeranian Voivodeships). Parts of the present-day federal state Brandenburg, such as Lower Lusatia and territory which had been Saxon until 1815, were not parts of the Mark. Colloquially but not accurately, the federal state Brandenburg is sometimes identified as the Mark or Mark Brandenburg.

The region was formed during the ice age, and characterized by moraines, glacial valleys, and numerous lakes. The territory is known as a Mark or march because it was a border county of the Holy Roman Empire (see also Margraviate of Meissen).

The Mark is defined by two uplands and two depressions. The depressions are taken up by rivers and chains of lakes with marsh and boggy soil along the shores; once used for peat collection, the riverbanks are now mostly drained and dry.^{[citation needed]}

The Northern or Baltic Uplands of the Mecklenburg Lake Plateau have only minor extensions into Brandenburg. The approximately 230 km-long range of hills in the Mark's south begins in the Lusatian Highlands (near Żary (Sorau)) and continues past Trzebiel (Triebel) and Spremberg, then to the northwest through Calau, and ends in the bare and dry Fläming. The southern depression is generally to the north of this ridge and appears strikingly in the Spreewald (between Baruth/Mark and Plaue an der Havel). The northern depression, lying almost directly south of the Baltic uplands, is defined by the lowlands of the Noteć and Warta Rivers, the Oderbruch, the valley of the Finow, the Havelland moor, and the Oder River.