| Louis III | |
| House: | Wittelsbach |
| Succession: | Elector Palatine |
| Reign: | 18 May 1410 – 30 December 1436 |
| Predecessor: | Rupert III |
| Successor: | Louis IV |
| Father: | Rupert of Germany |
| Mother: | Elisabeth of Nuremberg |
| Spouse: | Blanche of England Matilda of Savoy |
| Issue: | Mathilde Louis IV, Elector Palatine Frederick I, Elector Palatine Rupprecht |
| Birth Date: | 23 January 1378 |
| Death Place: | Heidelberg |
Louis III (German: Ludwig III. der Ältere or der Bärtige) (23 January 1378 - 30 December 1436), was an Elector Palatine of the Rhine from the house of Wittelsbach in 1410–1436.
Louis III was the third son of King Rupert of Germany and his wife Elisabeth of Nuremberg. During his father's campaign in Italy 1401-1402 Louis served as imperial vicar. He succeeded his father in 1410 as Elector of the Palatinate but did not run for the German crown. The Palatinate was divided among the four of Rupert's surviving sons. As oldest surviving son and new Prince-Elector Louis III received the main part, John received Palatinate-Neumarkt, Stephen received Palatinate-Simmern and Otto received Palatinate-Mosbach.
Louis III was a member of the Parakeet Society and of the League of Constance. Highly cultured and religious he was a patron of the Heidelberg University. Louis III acted as vicar for Sigismund, Holy Roman Emperor and was his bearer during the Council of Constance. As such Louis later also executed the sentences against Jan Hus and Jerome of Prague. He also arrested Antipope John XXIII in 1415.
Louis III returned very sick from a pilgrimage in 1427 into the Holy Land which he had organized after the death of his son Ruprecht. From 1430 onwards he was almost blind and in 1435 deprived of power by his wife and her advisors. In the following year he died, in Heidelberg, and was succeeded by his son Louis IV.
Louis III was married twice. Firstly, he married on 6 July 1402 Blanche of England (1392 - 22 May 1409), daughter of King Henry IV of England and Mary de Bohun. They had one son Ruprecht (22 June 1406 - 20 May 1426). This marriage brought the Palatine Crown into the hands of the Wittelsbach.
Secondly, he married on 30 November 1417 Matilda of Savoy, daughter of Amadeo, Prince of Achaea. They had five children: