It would be more semantically correct to say that Mark Twain contributed to American Literature than English, even though the term "English literature" is sometimes used to encompass all English-language literature. Regardless of what you call it, Twain's contributions to it cannot be overstated.

Twain's greatest contribution to American literature is no doubt The Adventures of Huckleberry Finn. It was the first major American work to use a vernacular style throughout and is still studied today, despite years of controversy over its subject matter. The book is one of the few to bear the distinction of being "The Great American Novel."

More than this, Twain was probably the first memorable literary voice that was truly "American." While the American authors that came before Twain could have just as easily have written what they did in England or Ireland, Twain used his childhood time on the Mississippi and humorist mastery to create a style of prose that was distinctly of the new world.

Samuel Langhorne Clemens, who recreated himself as Mark Twain the author, lecturer, traveler, and recorder of observations about the life and outlook of Americans in the 1800s, is one of the great American authors. His mastery of the use of dialects in his writing to convey the strength and personality of his characters is unparalleled. His descriptions of the places he visited and the adventures he had in those travels opened new areas to exploration in reality and vicariously through the reading of his works. Many of the stereotypical characteristics of the American psyche (willing to help each other, eager to take a risk for potential profit, outgoing and interested in taking part in new adventures) can be traced to the characters who lived in Twain's writings.