John Frederick (German: Johann Friedrich; 25 April 1625 in Herzberg am Harz – 18 December 1679 in Augsburg)[1] was duke of Brunswick-Lüneburg.

The third son of George, Duke of Brunswick-Lüneburg, John converted to the Roman Catholic Church, the only member of his family to do so, in 1651, as a result of a visit while in Italy to Saint Joseph of Cupertino.

[2] He received Calenberg when his elder brother George William inherited the Principality of Lüneburg.

In 1667, he employed as his master builder the Venetian architect Girolamo Sartorio, who designed many buildings in the town, including the Neustädter Kirche, and was instrumental in the expansion of the Herrenhausen Gardens.

In 1676, John Frederick employed Gottfried Wilhelm Leibniz as Privy Councillor and librarian of the important ducal library.