Ringling Bros. and Barnum & Bailey Circus was the joining together of two entertainment giants. The two circus companies had been operating independently for many years but merged in 1919 to form what they called "the Greatest Show on Earth."

In the 1860s, James Bailey and James Cooper formed the Cooper and Bailey Circus. About the same time, Dan Castello and William Coup had formed a circus in Wisconsin. In 1875, Castello and Coup engaged noted showman P.T. Barnum to lend his name to their circus, which became P.T. Barnum's Great Traveling Museum, Menagerie, Caravan, and Hippodrome.

One of the star attractions of the Cooper and Bailey Circus in the 1870s was a baby elephant named Columbia. Seeing the potential, Barnum tried to buy the elephant to use in his circus. The two circus companies merged in 1882, as the Barnum & Bailey Circus. The star of the show was Jumbo, which the circus said was the world's largest elephant.

Five brothers named Ringling (Al, Alf, Charles, John, and Otto) started a circus in Wisconsin in 1884. As did Barnum & Bailey, the Ringling Bros. Circus moved their circus from town town in animal-drawn caravans. As the popularity of both circus companies grew, they changed their transport method to the relatively new transportation method of rail. The Ringling brothers were seven in all; Henry joined in a couple of years, and Gus joined a few years after that.

Barnum died in 1891, and Bailey assumed sole ownership of the circus. A few years later, he embarked on a European tour, which lasted from 1897 to 1902. In the meantime, Ringling Bros. expanded their operations.

Bailey died in 1905, and Ringling Bros. bought its main competitor two years later. The Ringlings chose to operate both circus companies separately for a time, until merging them in 1919. Barnum & Bailey had added "Greatest Show on Earth" to its name awhile back, and the Ringling Bros. Circus had been advertised as the "World's Greatest Shows." On March 29, 1919, New York City saw the debut of Ringling Bros. and Barnum & Bailey Combined Shows. From then, advertisements for the circus shows also contained the words "Greatest Show on Earth."

The circus acts had long carried all of their own equipment, even down to the portable tents for which they were well known and the portable seating inside the tents. The last performance under the Big Top was on July 16, 1956, in Pittsburgh. Beginning in 1957, the circus moved to performing in permanent venues, such as arenas and sports stadiums, that already had seating and, in some cases, roofing.

The Ringling family sold the circus to Irvin Feld in 1967. Feld's brother Israel and Roy Hofheinz, a judge from Houston, were also owners. Irvin Feld began a clown college in 1968 and also bought a European circus and its star animal trainer, Gunther Gebel-Williams. Among Feld's other innovations was to split the circus into two touring units, Red and blue, which toured separately and offered different attractions.

The Felds and Hofheinz sold the circus to the toymaker Mattel in 1971 (with the Feld family retained as managers) but bought the circus back in 1982. Irvin Feld died in 1984, and his son Kenneth took over ownership, as part of Feld Entertainment.

Kenneth Feld announced in January 2017 that the circus would perform its final shows in May. Reasons given for the closing were higher costs and lower ticket sales.

The circus had also for many years been the target of allegations of poor treatment of animals.