It's a Small World (stylized in all lowercase and in quotations or with exclamation mark) is an Old Mill boat ride located in the Fantasyland area at various Disney theme parks around the world. Versions of the ride are installed at Disneyland in Anaheim, California; Magic Kingdom in Bay Lake, Florida; Tokyo Disneyland; Disneyland Park (Paris) and Hong Kong Disneyland. The inaugural version of the ride premiered at the 1964 New York World's Fair before permanently moving to Disneyland in 1966.

The ride features over 300 audio-animatronic dolls in traditional costumes from cultures around the world, frolicking in a spirit of international unity, and singing the attraction's title song, which has a theme of global peace. According to Time, the Sherman Brothers' song "It's a Small World" is the most publicly performed song of all time. In recent years, the Small World attractions at the various Disney parks have been updated to include depictions of Disney characters—in a design compatible with the original 1960s design of Mary Blair—alongside the original characters.

The ride was fabricated at the Walt Disney Studios in Burbank as Children of the World, and created by WED Enterprises. It was shipped to the 1964 New York World's Fair, where it was housed at the UNICEF pavilion (sponsored by Pepsi), which featured at its entrance a kinetic sculpture, The Tower of the Four Winds, a 120-foot perpetually spinning mobile created by WED designer Rolly Crump. The ride joined three other World's Fair attractions—Magic Skyway (Ford pavilion), Great Moments with Mr. Lincoln (Illinois pavilion), and The Carousel of Progress (General Electric pavilion)—that Disney was already involved with. All were intended to be dismantled and rebuilt at Disneyland after the World's Fair had closed in 1966.

Mary Blair was responsible for the attraction's whimsical design and color styling. The scenes and characters were conceived by animator Marc Davis, who also choreographed the audio-animatronic figures' dances. His wife Alice Davis designed the dolls' costumes. The costumes were heavily influenced by other countries' clothing, as Walt Disney had directed Alice Davis to "do whatever it takes to make these look like dolls every woman in the world would want to have". Crump designed the toys and other supplemental figures on display, as well as the original attraction's facade. The animated dolls were designed and sculpted by Blaine Gibson.

Arrow Development was heavily involved in the design of the passenger-carrying boats and propulsion system of the attraction. Two patents that were filed by Arrow Development staff and assigned to The Walt Disney Company illustrate passenger boats and vehicle guidance systems with features very similar to those later utilized on the Disneyland installation of the attraction. The firm is credited with manufacturing the Disneyland installation.

"Children of the World" was the working title of the attraction. Its soundtrack, composed by the Sherman Brothers, was originally supposed to feature the national anthems of every country represented throughout the ride; they were all played at once, resulting in cacophony. Walt conducted a walk-through of the attraction scale model with his staff songwriters Robert B. and Richard M. Sherman, saying, "I need one song that can be easily translated into many languages and be played as a round." The Sherman brothers then wrote "It's a Small World (After All)" in the wake of the 1962 Cuban Missile Crisis, which influenced the song's message of peace and brotherhood. When they first presented it to Walt, they played it as a slow ballad. Walt requested something more cheerful, so they increased the tempo and sang in counterpoint. Walt was so delighted with the final result that he renamed the attraction "It's a Small World" after the song. Recordings of the song were first sold in October 1964.

The Sherman Brothers originally wanted to donate all profits from "It's a Small World (After All)" to UNICEF, but Walt Disney dissuaded them from doing so, telling the brothers that the song would become popular. The Christian Science Monitor wrote of the song in 1967: "Visitors go away humming it as though they had made it up themselves." Robert B. Sherman's youngest son, Robert J. Sherman, has said that this song is the single most-performed and most-translated piece of music ever produced. In 2014, it was estimated that the song had played nearly 50 million times worldwide on the attractions alone, beating the radio and TV estimates for "You've Lost That Lovin' Feelin'" and "Yesterday", which were believed to have been played at least eight and seven million times, respectively. On average, the song is played 1,200 times during a 16-hour operating day.

A third verse celebrating the attraction's 45th anniversary was written and popularized, but not incorporated into the ride. In 2022, a 1964 recording of "It's a Small World (After All)" performed by the Disneyland Boys Choir was selected by the Library of Congress for preservation in the United States National Recording Registry as being "culturally, historically, or aesthetically significant". Shortly before his death, Richard Sherman composed a new verse to "It's a Small World". On November 27, 2024, Disney premiered it in a short film on ABC. On February 12, 2025, it was announced that the new verse would be added to the Disneyland version of the attraction starting on July 17, 2025, as part of Disneyland's 70th anniversary celebration and on July 7, 2025, it was announced that the Magic Kingdom version of the attraction would receive the new verse as well.