In the history of science fiction, the Golden Age is a period in which the genre is considered to have matured in American science fiction magazines, in particular Astounding Science Fiction—the period is usually referred to as the Golden Age of science fiction as a whole, though sometimes more specifically the Golden Age of Astounding. Its beginning is marked by John W. Campbell's assumption of the editorship of Astounding in the late 1930s. The end date is less agreed upon; it is often placed in the mid-1940s, though different definitions use dates ranging from 1941 to the early 1960s. Historiographically, the Golden Age follows the pulp era and precedes the New Wave.

Other eras have also been referred to as golden ages of science fiction in specific contexts. For instance, the 1950s are considered to be the golden age of science fiction cinema. A common humorous statement is that "The Golden Age of science fiction is twelve" years old, or thereabouts.

Science fiction magazines first appeared in 1926 with the launch of Hugo Gernsback's Amazing Stories. This is usually considered to be the beginning of the pulp era of science fiction, though definitions vary. Several additional magazines by Gernsback and others appeared, and in some cases disappeared again, in the years that followed; in 1937, there were seven science fiction pulp magazines in publication. In October 1937, John W. Campbell became editor of Astounding Stories. He finished the already in-progress December 1937 issue and started exercising direct editorial control from the January 1938 issue onwards alongside outgoing editor F. Orlin Tremaine, changing the title to Astounding Science Fiction starting with the March 1938 issue when he gained full editorial control. Campbell's editorship of Astounding is generally held to mark the beginning of the Golden Age, though the precise starting point varies slightly depending on definition—from 1937 at the earliest to 1940 at the latest.

Alva Rogers [Wikidata], in the 1964 book A Requiem for Astounding, writes that the period was both the Golden Age of science fiction as a whole and of Astounding in particular, and identifies the July 1939 issue as "the first real harbinger of Astounding's Golden Age". The July 1939 issue of Astounding has been adopted by others as the starting point of the Golden Age, and The Encyclopedia of Science Fiction writes that "The beginning of Campbell's particular Golden Age of SF can be pinpointed as the summer of 1939" more broadly. The July issue included "Black Destroyer", the first published story by A. E. van Vogt, as well as the first appearance by Isaac Asimov in the magazine with the story "Trends"; the August issue contained the first published story by Robert A. Heinlein, "Life-Line"; and the September issue had the first story by Theodore Sturgeon, "Ether Breather". Rogers nevertheless holds that, despite the appearance of these early stories, "it wasn't until 1940 that the Golden Age came into full being". Mike Ashley—who comments that the Golden Age of science fiction may be more appropriately referred to as the Golden Age of Astounding—similarly finds the July 1939 date arbitrary, viewing the change that happened as occurring gradually during 1938–1939 with each successive issue of Astounding contributing.

Campbell's instruction to his writers was refreshing: Write a story that could be published as a contemporary tale in a magazine published in the 25th century.
He also told them he wanted stories about aliens who could think as well as humans, but not like humans.

As editor of Astounding, Campbell took a proactive role. Even before he assumed the editorship, it had become the best-selling science fiction magazine and paid authors higher rates than its competitors did. This made Astounding a popular market and made it possible for Campbell to be selective. Campbell, who had been a science fiction writer before he became editor, had a strong sense of what made for good science fiction, and he would frequently demand revisions, revise himself, or outright reject stories that did not meet his exacting standards. One of his convictions was that the maturity of sf readership was greater than had previously been believed. He demanded that stories be logically sound, required greater scientific accuracy than had previously been the norm, and asked authors to consider what the effects of their ideas upon society and the individual would be. More broadly, he was not content with the prevailing literary quality that appeared in magazines at the time but insisted upon more proficient writing. In the words of Asimov, who started writing for Campbell around this time, "he found magazine science fiction childish, and he made it adult".

Campbell attracted some established writers such as Jack Williamson, Murray Leinster, and Clifford D. Simak; mainly, he discovered new ones like van Vogt, Asimov, Heinlein, and Sturgeon. He thus developed a stable of writers who were able to produce the kind of science fiction he wanted; authors who could not or would not write in Campbell's preferred style—the most high-profile example being Ray Bradbury—turned to his competitors instead. Campbell largely stopped writing himself, and instead frequently came up with ideas that he would have his writers turn into stories; for instance, Asimov credited Campbell with originating the plot for the 1941 short story "Nightfall", the underlying premise of the Foundation series, and the formulation of the Three Laws of Robotics. Lester del Rey later recalled a group of writers attempting to estimate the proportion of stories in Astounding that were based on Campbell's ideas, concluding that it must have exceeded half. Unlike many of his competitors at the time, Campbell was not expected by the publisher to write stories himself and was paid enough that it was not necessary for him to do so to supplement his income. He also only served as editor for Astounding (and, between 1939 and 1943, its fantasy companion Unknown), rather than needing to divide attention between multiple publications as several of his contemporaries did; Donald A. Wollheim credits Campbell's success as an editor in part to thus having time available to do the job with greater care. Michael R. Page, in The Cambridge History of Science Fiction, further points to Campbell being interested in science fiction for its own sake, rather than treating it solely as a business as the main science fiction editors before him (except Gernsback) had done.

By the late 1940s Astounding's dominance in the field was slowly beginning to be rivalled by Startling Stories, and the launch of The Magazine of Fantasy & Science Fiction in 1949 and Galaxy Science Fiction in 1950 ended it definitively. The 1950s saw the magazine market dominated by a triumvirate of Astounding, F&SF, and Galaxy. At the same time, the emergence of a new market for science fiction—books, especially paperbacks—shifted the genre's centre of gravity away from the magazines. Campbell's personal standing in the field also diminished. One reason was his increasing interest in various pseudoscientific concepts such as psionics and L. Ron Hubbard's Dianetics (a precursor to Scientology); Hubbard was one of Campbell's frequent contributors of fiction to both Astounding and Unknown, and in a controversial move, Campbell published his non-fiction article on Dianetics in the May 1950 issue of Astounding. Another was his hands-on editorial approach that many writers came to see as increasingly controlling rather than inspiring, leading them to publish elsewhere. A third was his political views, which grew increasingly overt, right-wing, and authoritarian—expressed in editorials that The Encyclopedia of Science Fiction suggests detracted his attention from collaborating with his writers—alienating a significant proportion of readers and writers alike.