A Voyage to Arcturus is a novel by the Scottish writer David Lindsay, first published in 1920. It combines fantasy, philosophy, and science fiction in an exploration of the nature of good and evil and their relationship with existence. Described by critic, novelist, and philosopher Colin Wilson as the "greatest novel of the twentieth century", it was a central influence on C. S. Lewis' Space Trilogy, and through him on J. R. R. Tolkien, who said he read the book "with avidity". Clive Barker called it "a masterpiece" and "an extraordinary work ... quite magnificent."

An interstellar voyage is the framework for a narrative of a journey through fantastic landscapes. The story is set at Tormance, an imaginary planet orbiting Arcturus, which in the novel (but not in reality) is a double star system, consisting of stars Branchspell and Alppain. The lands through which the characters travel represent philosophical systems or states of mind, through which the main character, Maskull, passes on his search for the meaning of life.

The book sold poorly during Lindsay's lifetime, but was republished in 1946 and many times thereafter. It has been translated into at least ten languages. Critics such as the novelist Michael Moorcock have noted that the book is unusual, but has been highly influential with its qualities of "commitment to the Absolute" and "God-questioning genius".