| Conventional Long Name: | Department of Mont-Tonnerre |
| Common Name: | Mont-Tonnerre |
| Year Start: | 1797 |
| Year End: | 1814 |
| Capital: | Mainz |
| Flag: | Flag of France |
| Image Map Caption: | Map of the former département du Mont-Tonnerre |
| Subdivision: | Department |
| Nation: | the First French Republic |
| P1: | Electorate of Mainz |
| Flag P1: | Banner of the Electorate of Mainz.svg |
| P2: | Prince-Bishopric of Speyer |
| Flag P2: | Wappen Bistum Speyer.png |
| Border P2: | no |
| P3: | Prince-Bishopric of Worms |
| Flag P3: | Wappen Bistum Worms.png |
| Border P3: | no |
| P4: | Nassau-Weilburg |
| Flag P4: | Blason Nassau-Weilbourg.svg |
| Border P4: | no |
| P5: | Landgraviate of Hesse-Darmstadt |
| Flag P5: | Flag of Hesse-Darmstadt Reiment during the Seven Years War (1756-1763).svg |
| P6: | Electoral Palatinate |
| Flag P6: | Flag of The Electoral Palatinate (1604).svg |
| S1: | Kingdom of Bavaria |
| Flag S1: | Flag of Bavaria (striped).svg |
| S2: | Grand Duchy of Hesse |
| Flag S2: | Flagge Großherzogtum Hessen ohne Wappen.svg |
| Today: | Germany |
Mont-Tonnerre (in French mɔ̃.tɔ.nɛʁ/) was a department of the First French Republic and later the First French Empire in present-day Germany. It was named after the highest point in the Palatinate, the Donnersberg ("Thunder Mountain", possibly referring to Donar, god of thunder). It was the southernmost of four departments formed in 1797 when the west bank of the Rhine was annexed by France. Prior to the French occupation, its territory was divided between the Archbishopric of Mainz, the Bishopric of Speyer, the Bishopric of Worms, Nassau-Weilburg, Hesse-Darmstadt, the Electorate of the Palatinate and the imperial cities of Worms and Speyer. Its territory is now part of the German states of Rhineland-Palatinate and Saarland. Its capital was Mainz (French: Mayence).
The department was subdivided into the following arrondissements and cantons (situation in 1812):[1]
Its population in 1812 was 342,316.[1]
After Napoleon was defeated in 1814, the department was divided between the Kingdom of Bavaria (Palatinate) and the Grand Duchy of Hesse (around Mainz).