The term Diet of Speyer refers to any of several sessions of the Diet of the Holy Roman Empire when it chose to meet in the city of Speyer, Germany. The most famous sessions occurred in 1526 and 1529.
Speyer was ceded to France in 1797 and to Bavaria in 1815.
Speyer, together with the territory of the bishops of Speyer W of the Rhine, was occupied by the French during the French Revolutionary Wars and formally ceded to France by the Treaty of Campo Formio (1797).
Speyer and the episcopal lands W of the Rhine were subsequently given to Bavaria at the Congress of Vienna (1815); they were incorporated into the Rhenish Palatinate, of which Speyer was the capital until 1945.