| Native Name: | Pfalzgrafschaft Simmern und Zweibrücken |
| Conventional Long Name: | Counties Palatine of Simmern and Zweibrücken |
| Common Name: | Palatinate-Simmern and Zweibrücken |
| Era: | Middle Ages |
| Status: | Vassal |
| Empire: | Holy Roman Empire |
| Government Type: | Principality |
| Year Start: | 1410 |
| Year End: | 1459 |
| Event Start: | Partitioned from Electoral Palatinate |
| Event1: | Inherited Veldenz |
| Date Event1: | 1444 |
| Event2: | Inheritance partitioned |
| Date Event2: | 1444 |
| Event End: | Partitioned in twain on death of Stephen |
| P1: | Electoral Palatinate |
| Flag P1: | Banner of the Palatinate.svg |
| P2: | County Palatine of Veldenz |
| Flag P2: | Wappen Grafschaft Veldenz.svg |
| Border P2: | no |
| S1: | House of Palatinate-Simmern |
| Flag S1: | Arms of the Palatinate (Palatinate-Bavaria)-Simmern.svg |
| Border S1: | no |
| S2: | Palatine Zweibrücken |
| Flag S2: | DEU Pfalz-Veldenz COA.svg |
| Border S2: | no |
| Capital: | Zweibrücken |
Palatinate-Simmern and Zweibrücken (German: Pfalz-Simmern-Zweibrücken) was a state of the Holy Roman Empire based in the Simmern and Zweibrücken in modern Rhineland-Palatinate, Germany.
Palatinate-Simmern and Zweibrücken was created in 1410 out of the partition of the Palatinate after the death of King Rupert III for his son Stephen. In 1444 the County of Veldenz was added to the state but later in the year Stephen partitioned his territories between his sons Frederick (who received Simmern) and Louis (who received Zweibrücken and Veldenz). In 1448, Stephen inherited half the territories of Palatinate-Neumarkt but sold them to Palatinate-Mosbach.