Tropic of Cancer is a novel by Henry Miller, first published in 1934 by Obelisk Press in Paris and still in print (Grove Press 1987 paperback: ISBN 0-8021-3178-6). Its publication in 1961 in the United States by Grove Press led to an obscenity trial that was one of several that tested American laws on pornography in the 1960s. While famous for its frank and often graphic depiction of sex, the book is also widely regarded as an important masterpiece of 20th century literature.

The novel is set in France (primarily Paris) during the 1930s. It is written in the first person, as are many of Miller's other novels, and often fluctuates between past and present tense. Some chapters follow a strict narrative and refer to Miller's actual friends, colleagues, and workplaces; others are written as stream-of-consciousness reflections. There are many passages explicitly describing the narrator's sexual encounters, but the book does not solely focus on this subject.

The novel included a preface credited to Anaïs Nin (although allegedly penned by Miller himself).

In 1964, the U.S. Supreme Court, in Grove Press, Inc., v. Gerstein, cited Jacobellis v. Ohio (which was decided the same day) and overruled state court findings of obscenity.

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