The Three Musketeers (French: Les Trois Mousquetaires) is a novel by Alexandre Dumas, first serialized in March–July 1844. Set in the 17th century, it recounts the adventures of a young man named d'Artagnan after he leaves home to travel to Paris, to join the Musketeers of the Guard. D'Artagnan is not one of the musketeers of the title; those are his friends Athos, Porthos, and Aramis, inseparable friends who live by the motto "all for one, one for all" ("tous pour un, un pour tous").

The story of d'Artagnan is continued in Twenty Years After and The Vicomte of Bragelonne: Ten Years Later. Those three novels by Dumas are together known as the d'Artagnan Romances.

The Three Musketeers was first published in serial form in the newspaper Le Siècle between March and July 1844.

When Alexandre Dumas wrote The Three Musketeers he also was a practising fencer and like many other French gentlemen of his generation he attended the schools for Canne de combat and Savate of Michel Casseux, Charles Lecour and Joseph Charlemont (who had been a regular fencing instructor in the French army).