Robert Anson Heinlein ( /ˈhaɪnlaɪn/ HYN-lyn) (July 7, 1907 – May 8, 1988) was an American science fiction writer. Often called the "dean of science fiction writers," he was one of the most influential and controversial authors of the genre in his time. He set a standard for scientific and engineering plausibility, and helped to raise the genre's standards of literary quality.

He was one of the first science fiction writers to break into mainstream magazines such as The Saturday Evening Post in the late 1940s. He was one of the best-selling science fiction novelists for many decades. He, Isaac Asimov, and Arthur C. Clarke are known as the "Big Three" of science fiction.

Heinlein, a notable writer of science fiction short stories, was one of a group of writers who came to prominence under the editorship of John W. Campbell, Jr. in his Astounding Science Fiction magazine—though Heinlein denied that Campbell influenced his writing to any great degree.

Within the framework of his science fiction stories, Heinlein repeatedly addressed certain social themes: the importance of individual liberty and self-reliance, the obligation individuals owe to their societies, the influence of organized religion on culture and government, and the tendency of society to repress nonconformist thought. He also examined the relationship between physical and emotional love, explored various unorthodox family structures, and speculated on the influence of space travel on human cultural practices. His approach to these themes led to wildly divergent opinions on what views were being expounded via his fiction.