Louis II, known as Louis the Stammerer (French: Louis le Bègue; 1 November 846 – 10 April 879), was the king of Aquitaine and later the king of West Francia. He was the eldest son of Emperor Charles the Bald and Ermentrude of Orléans. Louis the Stammerer was physically weak and outlived his father by a year and a half.

He succeeded his younger brother Charles the Child as the ruler of Aquitaine in 866 and his father in West Francia in 877, but he was never crowned emperor.

Louis was crowned king on 8 October 877 by Hincmar, archbishop of Reims, at Compiegne and was crowned a second time in August 878 by Pope John VIII at Troyes while the pope was attending a council there. The pope may have even offered him the imperial crown, but it was declined. Louis had relatively little impact on politics. He was described "a simple and sweet man, a lover of peace, justice, and religion". In 878, he gave the counties of Barcelona, Girona, and Besalú to Wilfred the Hairy. His final act was to march against the invading Vikings, but he fell ill and died on 9 April or 10 April 879, not long after beginning this final campaign. On his death, his realms were divided between his two sons, Carloman II and Louis III of France.