Collier's was an American general interest magazine founded in 1888 by Peter Fenelon Collier. It was launched as Collier's Once a Week, then renamed in 1895 as Collier's Weekly: An Illustrated Journal, shortened in 1905 to Collier's: The National Weekly and eventually to simply Collier's. The magazine ceased publication with the issue dated the week ending January 4, 1957, although a brief, failed attempt was made to revive the Collier's name with a new magazine in 2012.

As a result of Peter Collier's pioneering investigative journalism, Collier's established a reputation as a proponent of social reform. After lawsuits by several companies against Collier's ended in failure, other magazines joined in what Theodore Roosevelt described as "muckraking journalism." Founded by Nathan S. Collier, a descendant of Peter Collier, the Collier Prize for State Government Accountability was created in 2019. The annual US$25,000 prize is one of the largest American journalism prizes, and it was established to honor Peter Collier's legacy and contributions in the field of investigative reporting.

Peter F. Collier (1849–1909) left Ireland for the U.S. at age 17. Although he went to a seminary to become a priest, he instead started work as a salesman for P. J. Kenedy, publisher of books for the Roman Catholic market. When Collier wanted to boost sales by offering books on a subscription plan, it led to a disagreement with Kenedy, so Collier left to start his own subscription service. P. F. Collier & Son began in 1875, expanding into the largest subscription house in America with sales of 30 million books during the 1900–1910 decade.

With the issue dated April 28, 1888, Collier's Once a Week was launched as a magazine of "fiction, fact, sensation, wit, humor, news". It was sold with the biweekly Collier's Library of novels and popular books at bargain rates and as a stand-alone priced at seven cents. By 1892, with a circulation climbing past the 250,000 mark, Collier's Once a Week was one of the best selling magazines in the United States. The name was changed to Collier's Weekly: An Illustrated Journal in 1895 or the longer title Collier's Weekly: An Illustrated Journal of Art, Literature & Current Events. With an emphasis on news, the magazine became a leading exponent of the halftone news picture. To fully exploit the new technology, Collier recruited James H. Hare, one of the pioneers of photojournalism.

Collier's only son, Robert J. Collier, became a full partner in 1898.

By 1904, the magazine was known as Collier's: The National Weekly. Peter Collier died in 1909. When Robert Collier died in 1918, he left a will that turned the magazine over to three of his friends, Samuel Dunn, Harry Payne Whitney and Francis Patrick Garvan.

Robert J. Collier won a lawsuit against Postum Cereal Company and was awarded $50,000 in damages, but in 1912 an appeals court then handed down a majority decision that Postum deserved a new trial. The Postum Company believed that Collier's weekly used magazine coverage to attack their company's products in retaliation for not advertising in Collier's after Collier's wrote against a Grape-Nuts's claim that it was an "A Food for Brain and Nerves." Postum then bought advertising pages in major newspapers in retaliation.

The magazine was sold in 1919 to the Crowell Publishing Company, which in 1939 was renamed as Crowell-Collier Publishing Company.