As was his wont, at times O. Henry would slip into a story something specific from his life. In the story that leads off The Four Million, "Tobin's Palm," O. Henry makes a literary declaration. One of the characters in the story is a writer who comments: "I wander abroad by night seeking idiosyncrasies in the masses and truth in the heavens above. The rapid transit is poetry and art: the moon but a tedious, dry body, moving by rote." This is just as O. Henry did. "'Ye will put me in a book,' says Tobin, disgusted; 'will ye put me in a book?' 'I will not,' says the man,' for the covers will not hold ye. Not yet.'" O. Henry tried mightily to put the characters of New York into a book, and if he failed in his own eyes, he nonetheless succeeded better than any other short story writer of the day.

The Four Million, O. Henry's second collection of short stories, was the first to bear all the recognizable O. Henry traits. As he said in another of his books, he was the voice of the city, giving it expression and reality. New York was the gateway to America then, and immigrants were pouring in from all parts of the world. O. Henry celebrated that ethnic diversity.

O. Henry was the conscience of the city, too. He not only spoke eloquently of the plight of the poor in such stories as "The Skylight Room" and "An Unfinished Story," but he brought romance and adventure, excitement and glamour to those who had too little of it in their lives.

What made O. Henry a thoroughly American artist was his conviction of the essential benevolence of life. Put another way, he was the spokesman for the American Dream. He wrote for an audience that was not far removed from the immigrant experience; if they were not immigrants themselves, probably their parents were. America was a country of immigrants. Most of them came to America looking for a better life. True, they often found poverty, but there was also hope, and O. Henry gave expression to that ideal in his fiction. Despite the vastness of the city, lost lovers can be reunited as they are in "Tobin's Palm" and "Springtime a la Carte," a young woman can be rescued from suicide in "The Skylight Room," and true love can win out in "An Adjustment of Nature" and "Mammon and the Archer." In "The Green Door" adventure and romance beckon. Despite poverty, the lovers have each other in "The Gift of the Magi" and in "A Service of Love," and that is more than enough, O. Henry maintains. In "Lost on Dress Parade" and "The Coming-Out of Maggie" the characters filch a bit of glamour for their otherwise drab lives.

Still, tragedy is rarely far away. "Life is made up of sobs, sniffles, and smiles, with sniffles predominating," O. Henry wrote. That may sound coy, but suicide is the conclusion of "The Furnished Room," made more tragic by callous indifference, and in "An Unfinished Story" it is clear that degradation is not far ahead, the result of loneliness, despair, and poverty.

O. Henry's writing is irrevocably linked with the surprise ending. Indeed, the term "O. Henry ending" has entered the literary vocabulary. However, the O. Henry ending was not merely something tacked onto the body of the story to astound the reader, it was a natural illumination of character. The surprise ending was an expression of his philosophy of life. Take, for instance, the well-known "The Gift of the Magi," the second story of The Four Million. The surprise ending not only epitomizes the character of these two self-sacrificing lovers, but it also epitomizes the character of love itself, the very theme of O. Henry's story. Theme and character are embodied in the surprise that really is not a surprise lurking at the end.

In the same way the climax of "The Love-Philtre of Ikey Schoenstein" drives home the point of the story. Ikey, using his wiles, tries to trick his rival and gain the heart of his beloved. But his rival, more honest than Ikey, adheres to the philosophy "if you get the girl get her on the square." At the surprising conclusion, Ikey discovers that he has failed precisely because he is not on the square. Ikey may not be any wiser, but the readers are.

O. Henry's works have been most closely identified with the short fiction of Guy de Maupassant and Anton Chekhov. All three were prolific in the shorter forms, writing stories frequently of the lower class, and often using the slice of life story for revelation. But there is an amorality about Maupassant and a fatalism about Chekhov that O. Henry would have been unable to accept. Many American writers have attempted to emulate the slangy storytelling of O. Henry, few as successfully as Ring Lardner.

Intentional or not, The Trimmed Lamp (1907) seems to sound a darker note than The Four Million. Alongside the light-hearted stories, there are many tales of despair. Often in these stories a sudden gush of pain will erupt. At times a story ends on a note of bleak tragedy and hopelessness. The word "lost" echoes time and again. "Brick-dust Row" ends with: "But man, it's too late, I tell you. It's too late. It's too late. It's too late." The story of "Elsie in New York" tells of young girls who are "lost thus around us every day." "The Guilty Party" chronicles the neglect of a young child, who eventually kills her lover and commits suicide. The hero of "The Assessor of Success" concludes with a cry of despair, "God! I wish I could die."

Once again O. Henry presents a kaleidoscope of characters; the millionaire, the bum, the shop-girl, the bohemian, the artist, the gang member, the tourist, all are here in abundance, all seeking elusive happiness. O. Henry's forte was not the closely and deeply drawn character. Within the confines of the short story, in a couple of thousand words, he painted his characters with swift and broad strokes. What O. Henry lacked in subtlety, he made up for in penetrating insight, honest emotion, and keen, good humor.

O. Henry brought Romanticism squarely into the twentieth century. He showed that industrialism and Romanticism were not incompatible. The gritty aspects of modern city life — "the crash of the elevated trains, clanging cars," smoky factories, bums on park benches, and department stores — all formed the fabric of his fiction. He thrust this seemingly fragile and delicate art into the hustle and bustle of the streets, into the squalor of the tenements, the dingy apartments of shop girls, and the furnished rooms of transients. Romanticism not only survived, it flourished under his pen. O. Henry protested against the "club of realism." Alongside the negative aspects of the city, there was also much that was positive. There was glamour, excitement, and the endless variety of the urban experience.

Central to O. Henry's conception of life is the question, "What's around the corner?" For O. Henry, the future represented a challenge; it was magical, brimming with excitement, with the possibility of surprise. A policeman could be a millionaire tomorrow; a shop-girl could fall in love and marry a wealthy young gentleman. This was the Land of Opportunity, and Americans had great faith in the vision of social mobility; wealth and fame could be attained by anybody with the talent, ability, and perseverance.

Good or bad, happiness or sorrow, the moral fulcrum of an O. Henry story is often equally balanced. In "The Trimmed Lamp" the goodness of Nancy who refuses to be "a traitor to herself" is balanced against Lou who becomes a wealthy man's mistress. In "The Last Leaf," Johnsy's gallant struggle against death is weighted against Old Behrman, who dies helping her by painting the last leaf on the window.

A light-hearted writer, O. Henry was unafraid to address many of the pressing issues of the day: alcoholism, poverty, child neglect, poor housing, working single women. Yet as he chronicled these stories, he knew the problems might be insoluble. The conclusion of "The Trimmed Lamp" has a policeman walking his beat, ignoring a weeping woman: "He was wise enough to know that these matters are beyond help so far as the power he represents is concerned, though he rap the pavement with his nightstick till the sound goes up to the furthermost stars."

One of the trademarks of O. Henry is the way in which pithy gems of observation and insight are scattered throughout a story — "the raisins in the dough of existence," he called it. For instance, in the title story from The Trimmed Lamp, O. Henry makes the following observation: "If you live in an atmosphere of luxury, luxury is yours whether your money pays for it, or another's." Or he describes the dull, but dependable Dan "in his neat but obviously ready-made suit, his ready-made tie and unfailing, genial, ready-made wit." Or a line or two later O. Henry says, "He was of that good kind that you are likely to forget while they are present, but remember distinctly after they are gone."

O. Henry loved to play with the English language. His stories are filled with malapropisms, outrageous puns, silly jokes, and light-hearted slang. Sometimes the stories are so slangy that the reader — not familiar with turn-of-century phrases — can miss the point.

The best-known adaptation of the stories of O. Henry is a 1952 film titled O. Henry's Full House, released by Twentieth Century Fox. Cast and production were first-rate. John Steinbeck introduced the five stories: "The Cop and the Anthem," screenplay by Lamar Trotti, directed by Henry Koster, starring Charles Laughton, David Wayne, and Marilyn Monroe; "The Clarion Call," screenplay by Richard Breen, directed by Henry Hathaway; starring Dale Robertson and Richard Widmark; "The Last Leaf," screenplay by Ivan Coff and Ben Roberts, directed by Jean Negulesco, starring Anne Baxter, Jean Peters, and Gregory Ratoff; "The Ransom of Red Chief," screenplay by Nunnally Johnson, directed by Howard Hawks, starring Fred Allen and Oscar Levant; and "The Gift of the Magi," screenplay by Walter Bullock, directed by Henry King, starring Jeanne Crain and Farley Granger.

Hollywood has also extensively used the O. Henry character The Cisco Kid in twenty-three films — sound and silents — with varying degrees of authenticity. Besides films, there was also a 1950s television series, The Cisco Kid, starring Duncan Renaldo.

A number of O. Henry stories have been filmed over the years. Most are just titles, now, but a few are still remembered: The Green Door, 1917; An American Live Wire, 1918; Everybody's Girl, 1918; You're Fired, 1919; Alias Jimmy Valentine, 1920; The Texan, 1930; Doctor Rhythm, 1938; Llano Kid, 1940; Black Eagle, 1948; and The Big Chief, April 1960.

In 1957 there was a television series based upon the short stories of O. Henry. It was titled The O. Henry Playhouse. The thirty-minute anthology, hosted by Thomas Mitchell, lasted for thirty-nine episodes. Among the stories adapted for the small screen were "Georgia's Ruling," "Between Rounds," and "Hearts and Hands."