The Principality of Bayreuth or Margraviate of Brandenburg-Bayreuth was an immediate territory of the Holy Roman Empire, ruled by a Franconian branch of the Hohenzollern dynasty. Since Burgrave Frederick VI of Nuremberg was enfeoffed with the Margraviate of Brandenburg in 1415/17, the Hohenzollern princes transferred the margravial title to their Franconian possessions, though the principality never had been a march. Until 1604 they used Plassenburg Castle in Kulmbach as their residence, hence their territory was officially called the Principality of Kulmbach or Margraviate of Brandenburg-Kulmbach until the Empire's dissolution in 1806.

Frederick was the last Burgrave of Nuremberg from 1397 to 1427, Margrave of Brandenburg-Ansbach from 1398, Margrave of Brandenburg-Kulmbach from 1420, and Elector of Brandenburg from 1415 until his death. He became the first member of the House of Hohenzollern to rule the Margraviate of Brandenburg.