Not all that we see on-screen of Paris is Paris. The square where Gene Kelly sells his paintings to a wealthy American woman in "An American in Paris" is a soundstage in Hollywood. So is the rue St. Denis in the old Les Halles market where Shirley Maclaine streetwalks in Billy Wilder's "Irma la Douce." And the outdoor cafe in "April in Paris." And Notre Dame Cathedral in the 1939 version of "The Hunchback of Notre Dame." But it hardly matters. So much of Hollywood's version of Paris is fantasy, a place where the line between the real and the imagined is delightfully blurred, where adventure, mystery, beauty and even love lurk just around the corner. (The filmmaker Ernst Lubitsch, who made a dozen films in the 1920s and 1930s using fake Paris, even preferred it to the real. "I've been to Paris, France, and I've been to Paris Paramount," he said. "Paris Paramount is better.") Now Paris is celebrating the American film industry's love affair with the City of Light with "Paris Viewed by Hollywood," an exhibition that brings together film clips, posters, photographs, paintings, costumes, documents and memorabilia from 100 movies about or set in Paris. Since 1900, about 800 American films have been set in Paris. The show moves chronologically from silent to 3-D, starting with Thomas Edison's jerky black-and-white images shot from a boat in the Seine in 1910 and ending with Martin Scorsese's "Hugo." Fans of the latter film should look for two resin statues of ghosts built for the cemetery scene. It is on loan from Paris's Cinémathèque Française, a 14,700-square-foot building designed by Frank Gehry dedicated to the preservation, restoration and showing of films. Scorsese himself drew heavily on the Cinémathèque's vast collection of films and ephemera from the director Georges Méliès, and as a gesture of thanks he gave it the automaton that father and son contemplate at the beginning of the movie. City Hall, the host of the show, has built a 42-foot-long screen in its Salle St. Jean to project scenes from several films: Greta Garbo discussing the number of steps to the top of the Eiffel Tower in "Ninotchka"; Fred Astaire, Audrey Hepburn and Kay Thompson singing at the top of the Eiffel Tower in "Funny Face"; and Gene Kelly and Leslie Caron dancing dreamily in "An American in Paris." It's a particular delight to observe the ways Hollywood has portrayed Paris over the years - "Absinthe," a 13-minute silent film from 1913, depicts the decadent, alcohol-sodden bohemian lifestyle of the late-19th century - and how it used the city to experiment with risqué themes that would be off-limits in American settings. In Lubitsch's 1933 adaptation of the Noel Coward play "Design for Living," Miriam Hopkins, Fredric March and Gary Cooper play a sophisticated trio involved in a romantic triangle - they both want her and she wants both of them. The three of them end up living together, in Paris. "Desire, libertine living, prostitution, illicit love - Paris was the place without taboo for Hollywood," said Antoine de Baecque, a film historian and the exhibition's curator. Baecque has also pulled together costumes including a gold-sequined ball gown from the musical "Lovely to Look At" (1952); Greta Garbo's black velvet gloves with angled cuffs, sequins and rhinestones from "Camille" (1936); Gene Kelly's brown suede dancing boots from "The Three Musketeers" (1948); and the bolero jacket Hubert de Givenchy made for Audrey Hepburn in "Love in the Afternoon" (1957). Among the other objects are three "mood boards" for Woody Allen's "Midnight in Paris," the studies for the pastry confections in Sofia Coppola's "Marie-Antoinette," and Mary Pickford's receipt for lunch for two at the Ritz. The city-run museum is free, so the wait to get into the show, which runs until Dec. 15, can be long. So if you can't get in (or even if you can), head to the Cinémathèque Française in the 12th Arrondissement. On Oct. 23, it will open an exhibit exploring the 1945 French classic "Children of Paradise," directed by Marcel Carné, with paintings, photographs, documents, costumes and audiovisual clips that examine the film in various aspects, including how it came to be made during the German occupation of Paris. "It's the most beautiful film on Paris and on Paris in film," said Jean-Christophe Mikhaïloff, the Cinémathèque's director of development. It's a great French superproduction - our 'Gone With the Wind.' In the meantime, every day for several weeks starting Oct. 3, the cinema Le Champo in the Latin Quarter will show a different Hollywood film set wholly or partially in Paris. Among them will be Stanley Donen's "Charade"; three Lubitsch films, including "The Eighth Wife of Blue Beard"; Billy Wilder's "Love in the Afternoon"; Howard Hawks's "Gentlemen Prefer Blondes"; and Roman Polanski's "The Ninth Gate." And for strollers, there's "Paris Movie Walks" - both a book and an iPhone app - that offers guided walking tours through the city along with delicious movie trivia. My favorite: What restaurant was booked solid for months by American tourists after its signature roast chicken was featured in a film? Answer: Le Grand Colbert, the setting for the dinner scene in "Something's Gotta Give," with Diane Keaton, Jack Nicholson and Keanu Reeves. Perhaps the most cutting-edge screening room in Paris is also the most exclusive: Warner Brothers installed it recently in the residence of American Ambassador Charles H. Rivkin. Rivkin, the former president and C.E.O. of entertainment companies like The Jim Henson Company (Remember the "Muppets"?), is crazy about movies. An original poster from "An American in Paris" hangs in his outer office in the embassy. When Woody Allen was in Paris filming "Midnight in Paris," Rivkin hosted him and his family in the residence for a week. When the film "Julie and Julia," about the American chef Julia Child had its premiere in France, he held a reception for Nora Ephron, Meryl Streep and the Cordon Bleu cooking school, which gave them honorary degrees. He hosted a dinner for Clint Eastwood in honor of his decoration as commander of the Legion of Honor and brought the actor Samuel L. Jackson into the troubled suburbs to meet local residents as part of a cultural outreach program. Rivkin has organized meetings with dozens of aspiring artists, directors and writers from the suburbs with the actress and director Jody Foster and Allen. When Rivkin arrived as ambassador in 2009, he even used Hollywood to charm Nicolas Sarkozy, then the president. In Sarkozy's speech to the United States Congress two years before, he had expressed his love for American movies and admiration for stars like John Wayne and Rita Hayworth. Rivkin sent him an unreleased publicity poster of Hayworth set in an Art Deco frame. When Rivkin formally presented his diplomatic credentials at the Élysée Palace afterward, Sarkozy purred, "I adore that photo."