The Protestant Union, also known as the Evangelical Union, Union of Auhausen, German Union or the Protestant Action Party, was a coalition of Protestant German states. It was formed on 14 May 1608 by Frederick IV, Elector Palatine in order to defend the rights, land and safety of each member. It included both Calvinist and Lutheran states, and dissolved in 1621.

Frederick IV, Elector Palatine of the Rhine, only surviving son of Louis VI, Elector Palatine and Elisabeth of Hesse, called "Frederick the Righteous".