The Age of Innocence is a novel by American author Edith Wharton, published on 25 October 1920. It was her eighth novel, and was initially serialized in 1920 in four parts, in the magazine Pictorial Review. Later that year, it was released as a book by D. Appleton & Company. It won the 1921 Pulitzer Prize for Fiction, making Wharton the first woman to win the prize. Though the committee had initially agreed to give the award to Sinclair Lewis for Main Street, the judges, in rejecting his book on political grounds, "established Wharton as the American 'First Lady of Letters'". The story is set in the 1870s, in upper-class, "Gilded Age" New York City. Wharton wrote the book in her 50s, after she was already established as a major author in high demand by publishers.

The Age of Innocence, which was set in the time of Wharton's childhood, was a softer and gentler work^{[attribution needed]} than The House of Mirth, which Wharton had published in 1905. In her autobiography, Wharton wrote that The Age of Innocence had allowed her to find "a momentary escape in going back to my childish memories of a long-vanished America... it was growing more and more evident that the world I had grown up in and been formed by had been destroyed in 1914." Scholars and readers alike agree that The Age of Innocence is fundamentally a story that struggles to reconcile the old with the new.

Wharton was raised in the old world of rigid and proper New York society, which features in the story. She had spent her middle years, including the whole of World War I, in Europe, where the devastation of a new kind of mechanized warfare was felt most deeply. As explained by Millicent Bell in the Cambridge companion to Wharton, "The Age of Innocence was composed and first read in the aftermath of [Theodore] Roosevelt's death and in the immediate wake of World War I. We frame the ending remembering the multiple losses... not only the loss of Roosevelt but the destruction of the prewar world and all that Wharton valued in it."

The Age of Innocence centers on an upper-class couple's impending marriage, and the introduction of the bride's cousin, plagued by scandal, whose presence threatens their happiness. Though the novel questions the assumptions and morals of 1870s New York society, it never develops into an outright condemnation of the institution. The novel is noted for Wharton's attention to detail and its accurate portrayal of how the 19th-century East Coast American upper class lived, as well as for the social tragedy of its plot. Wharton was 58 years old at publication; she had lived in that world and had seen it change dramatically by the end of World War I.

The title is an ironic comment on the polished outward manners of New York society when compared to its inward machinations. It is believed to have been drawn from the popular painting A Little Girl by Sir Joshua Reynolds that later became known as The Age of Innocence (though Reynolds himself never called it that; the title was given by the engraver Joseph Grozer in 1794), and was widely reproduced as the commercial face of childhood in the later half of the 18th century. The title, while ironic, was not as caustic as the title chosen for The House of Mirth, which Wharton had published in 1905.

The story opens in the 1870s with Newland Archer, gentleman lawyer and heir of one of New York City's most illustrious families, happily anticipating his highly desirable marriage to the sheltered, shallow and beautiful May Welland. But he finds reason to doubt his choice of bride after the appearance of Countess Ellen Olenska, May's exotic and fascinating cousin. Ellen strikes Archer as the opposite of the innocent and ignorant May. She has returned to New York from Europe after scandalously separating herself from a disastrous marriage to a Polish count. At first, Ellen's arrival and its potential effect on the reputation of his bride-to-be's family disturbs Newland, but he becomes intrigued by Ellen, who brazenly flouts New York society's fastidious rules. As Newland's admiration for her grows, so do his doubts about marrying May, a perfect product of Old New York society; the match no longer seems the ideal fate he had imagined.

Ellen's decision to divorce Count Olenski causes a social crisis for the other members of her family, who are terrified of scandal and disgrace. Living apart can be tolerated, but divorce is unacceptable. To save the Wellands' reputation, a law partner of Newland asks him to dissuade Ellen from going through with the divorce. He succeeds, but in the process comes to care for her. Afraid of falling in love with Ellen, Newland begs May to elope and accelerate their wedding date, but she refuses.

Some weeks later, Newland tells Ellen he loves her; Ellen reciprocates, but is horrified that their love will hurt May, and does not want him to leave May for her. Newland receives May's telegram agreeing to wed sooner.