The Imperial Diet (Latin: Dieta Imperii or Comitium Imperiale; German: Reichstag) was the deliberative body of the Holy Roman Empire.

It was not a legislative body in the contemporary sense; its members envisioned it more like a central forum where it was more important to negotiate than to decide.

In the early and high Middle Ages these assemblies were not yet institutionalized, but were held as needed at the decision of the king or emperor.

After the conquest of Italy, the 1158 Diet of Roncaglia finalized four laws that would significantly alter the (never formally written) constitution of the Empire, marking the beginning of the steady decline of the central power in favour of the local dukes.

In contrast, this process was hastened with the Peace of Westphalia of 1648, which formally bound the Emperor to accept all decisions made by the Diet, in effect depriving him of his few remaining powers.

The Habsburg Emperors possessed a large number of votes, and even held command over the Reichsarmee (Imperial Army) if the Diet decided to raise it.

The seven Prince-electors were designated by the Golden Bull of 1356: The number increased to eight, when in 1623 the Duke of Bavaria took over the electoral dignity of the Count Palatine, who himself received a separate vote in the electoral college according to the 1648 Peace of Westphalia (Causa Palatina), including the high office of an Archtreasurer.

In the War of the Bavarian Succession, the electoral dignities of the Palatinate and Bavaria were merged, approved by the 1779 Treaty of Teschen.

In turn, four secular princes were elevated to prince-electors: These changes however had little effect, as with the abdication of Francis II as Holy Roman Emperor the Empire was dissolved only three years later.

As the Austrian House of Habsburg had failed to assume the leadership of the secular bench, they received the guidance over the ecclesiastical princes.

The first ecclesiastical prince was the Archbishop of Salzburg as Primas Germaniae; the Prince-Archbishop of Besançon, though officially a member until the 1678 Treaty of Nijmegen, did not attend the Diet's meetings.

The Prince-Bishopric of Lübeck remained an ecclesiastical member even after it had turned Protestant, ruled by diocesan administrators from the House of Holstein-Gottorp from 1586.

The college was led by the city council of the actual venue until the Perpetual Diet in 1663, when the chair passed to Regensburg.

At meetings of the Protestant body, Saxony would introduce each topic of discussion, after which Brandenburg-Prussia and Hanover would speak, followed by the remaining states in order of size.

A volume dealing with the 1532 Diet of Regensburg, including the peace negotiations with the Protestants in Schweinfurt and Nuremberg, by Rosemarie Aulinger of Vienna was published in 1992.