Weird Tales is an American fantasy and horror fiction pulp magazine founded by J. C. Henneberger and J. M. Lansinger in late 1922. The first issue, dated March 1923, appeared on newsstands February 18. The first editor, Edwin Baird, printed early work by H. P. Lovecraft, Seabury Quinn, and Clark Ashton Smith, all of whom went on to be popular writers, but within a year, the magazine was in financial trouble. Henneberger sold his interest in the publisher, Rural Publishing Corporation, to Lansinger, and refinanced Weird Tales, with Farnsworth Wright as the new editor. The first issue to list Wright as editor was dated November 1924. The magazine was more successful under Wright, and despite occasional financial setbacks, it prospered over the next 15 years. Under Wright's control, the magazine lived up to its subtitle, "The Unique Magazine", and published a wide range of unusual fiction.

Lovecraft's Cthulhu mythos stories first appeared in Weird Tales, starting with "The Call of Cthulhu" in 1928. These were well-received, and a group of writers associated with Lovecraft wrote other stories set in the same milieu. Robert E. Howard was a regular contributor, and published most of his Conan the Barbarian stories in the magazine, and Seabury Quinn's series of stories about Jules de Grandin, a detective who specialized in cases involving the supernatural, was very popular with the readers. Other well-liked authors included Nictzin Dyalhis, E. Hoffmann Price, Robert Bloch, and H. Warner Munn. Wright published some science fiction, along with the fantasy and horror, partly because when Weird Tales was launched, no magazines were specializing in science fiction, but he continued this policy even after the launch of magazines such as Amazing Stories in 1926. Edmond Hamilton wrote a good deal of science fiction for Weird Tales, though after a few years, he used the magazine for his more fantastic stories, and submitted his space operas elsewhere.

In 1938, the magazine was sold to William Delaney, the publisher of Short Stories, and within two years, Wright, who was ill, was replaced by Dorothy McIlwraith as editor. Although some successful new authors and artists, such as Ray Bradbury and Hannes Bok, continued to appear, the magazine is considered by critics to have declined under McIlwraith from its heyday in the 1930s. Weird Tales ceased publication in 1954, but since then, numerous attempts have been made to relaunch the magazine, starting in 1973. The longest-lasting version began in 1988 and ran with an occasional hiatus for over 20 years under an assortment of publishers. In the mid-1990s, the title was changed to Worlds of Fantasy and Horror because of licensing issues, the original title returning in 1998.

The magazine is regarded by historians of fantasy and science fiction as a legend in the field, Robert Weinberg considering it "the most important and influential of all fantasy magazines". Weinberg's fellow historian, Mike Ashley, describes it as "second only to Unknown in significance and influence", adding that "somewhere in the imagination reservoir of all U.S. (and many non-U.S.) genre-fantasy and horror writers is part of the spirit of Weird Tales".

In the late 19th century, popular magazines typically did not print fiction to the exclusion of other content: they would include nonfiction articles and poetry as well. In October 1896, Frank A. Munsey Company's Argosy magazine was the first to switch to printing only fiction, and in December of that year, it changed to using cheap wood-pulp paper. This is now regarded by magazine historians as having been the start of the pulp magazine era. For years, pulp magazines were successful without restricting their fiction content to any specific genre, but in 1906, Munsey launched Railroad Man's Magazine, the first title that focused on a particular niche. Other titles that specialized in particular fiction genres followed, starting in 1915 with Detective Story Magazine, with Western Story Magazine following in 1919. Weird fiction, science fiction, and fantasy all appeared frequently in the pulps of the day, but by the early 1920s, still no single magazine was focused on any of these genres, though The Thrill Book, launched in 1919 by Street & Smith with the intention of printing "different", or unusual, stories, was a near miss.

In 1922, J. C. Henneberger, the publisher of College Humor and The Magazine of Fun, formed Rural Publishing Corporation of Chicago, in partnership with his former fraternity brother, J. M. Lansinger. Their first venture was Detective Tales, a pulp magazine that appeared twice a month, starting with the October 1, 1922 issue. It was initially unsuccessful, and as part of a refinancing plan, Henneberger decided to publish another magazine that would allow him to split some of his costs between the two titles. Henneberger had long been an admirer of Edgar Allan Poe, so he created a fiction magazine that would focus on horror, and titled it Weird Tales.

Henneberger chose Edwin Baird, the editor of Detective Tales, to edit Weird Tales; Farnsworth Wright was first reader, and Otis Adelbert Kline also worked on the magazine, assisting Baird. Payment rates were low, usually between a quarter and a half cent per word; the budget went up to one cent per word for the most popular writers. Sales were initially poor, and Henneberger soon decided to change the format from the standard pulp size to large pulp, to make the magazine more visible. This had little long-term effect on sales, though the first issue at the new size, dated May 1923, was the only one that first year to sell out completely—probably because it contained the first instalment of a popular serial, The Moon Terror, by A.G. Birch.

Even before the launch, Rural had incurred higher than expected costs from the printer for the first few issues of Detective Tales. After the first issue of Weird Tales, Rural switched to a cheaper printer, but it meant that the magazine began at a financial disadvantage. The magazine lost a considerable amount of money under Baird's editorship: after thirteen issues, the total debt was over $40,000 and perhaps as much as $60,000. In the meantime, Detective Tales had been retitled Real Detective Tales and was making a profit, as was College Humor. Henneberger decided early in 1924 on a reorganization of the editorial staff, which meant that by late spring Baird was no longer actively editing Weird Tales, though for a while he remained on the staff. A financial reorganization was also necessary, and Henneberger decided to sell both magazines to Lansinger and invest the money in Weird Tales. This did not address the debt, $43,000 of which was owed to the magazine's printer, Cornelius Printing Company. Cornelius agreed to an arrangement in which they would control a new company, to be called Popular Fiction Publishing, until the debt was paid off. Not all of the magazine's debts were eliminated by this transaction, but it meant that Weird Tales could continue to publish, and perhaps return to profitability. The business manager of the new company was William (Bill) Sprenger, who had been working for Rural Publishing. Henneberger had hopes of eventually refinancing the debt with the help of another printer, Hall Printing Company, owned by Robert Eastman, though it is not known when Eastman and Henneberger discussed the possibility.