The Trespasser is a 1912 novel by D. H. Lawrence. Set mostly on the Isle of Wight, it tells the story of Siegmund, a married man with children, and his adulterous affair with Helena.

Originally it was titled the Saga of Siegmund and drew upon the experiences of a friend of Lawrence, Helen Corke, and her adulterous relationship with a married man that ended with his suicide. Lawrence worked from Corke's diary, with her permission, but also urged her to publish; which she did in 1933 as Neutral Ground.

The biographer Brenda Maddox writes in D. H. Lawrence: The Story of a Marriage (1994) that The Trespasser was reviewed by the translator Constance Garnett, who found its last fifty pages comparable in quality to the work of "the best Russian school."^[2]

Lawrence's novel was adapted into a 1981 television film starring Alan Bates as Siegmund; Pauline Moran as Helena; Margaret Whiting as Beatrice, wife of Siegmund; and Dinah Stabb as Louisa, Helena's friend; among others. It was directed by Colin Gregg and written by Hugh Stoddart.

• The Trespasser (1912), edited by Elizabeth Mansfield, Cambridge University Press, 1981, ISBN 0-521-22264-8