As the editor of the magazine Astounding, John W. Campbell was perhaps the most influential figure in mid-century science fiction. He helped define and refine the field, and he launched the careers of notable writers such as Isaac Asimov and Robert Heinlein. He was, however, a controversial figure. Furthermore, he continued to promote ideas rooted in pseudoscience. In this chapter we consider Campbell’s editorship and examine some reasons why his influence began to wane.