The Duchy of Brunswick-Lüneburg, or more properly the Duchy of Brunswick and Lüneburg, was a historical duchy that existed from the late Middle Ages to the Late Modern era within the Holy Roman Empire, until the year of its dissolution. The duchy was located in what is now northwestern Germany. Its name came from the two largest cities in the territory: Brunswick and Lüneburg.

The House of Hanover is a European royal house with roots tracing back to the 17th century. Its members, known as Hanoverians, ruled Hanover, Great Britain, Ireland, and the British Empire at various times during the 17th to 20th centuries. Originating as a cadet branch of the House of Welf in 1635, also known then as the House of Brunswick-Lüneburg, the Hanoverians ascended to prominence with Hanover's elevation to an Electorate in 1692. In 1714 George I, prince-elector of Hanover and a descendant of King James VI and I, assumed the throne of Great Britain and Ireland, marking the beginning of Hanoverian rule over the British Empire. At the end of his line, Queen Victoria's death in 1901, the throne of the United Kingdom passed to her eldest son Edward VII, a member of the House of Saxe-Coburg and Gotha, through his father Albert, Prince Consort. The last reigning members of the House of Hanover lost the Duchy of Brunswick in 1918 when Germany became a republic.