“If was an American science fiction magazine launched in March 1952 by Quinn Publications, owned by James L. Quinn. The magazine was moderately successful, though it was never regarded as one of the first rank of science fiction magazines. It achieved its greatest success under editor Frederik Pohl, winning the Hugo Award for best professional magazine three years running from 1966 to 1968. If was merged into Galaxy Science Fiction after the December 1974 issue, its 175th issue overall.”
You can now read If magazine for free at Internet Archive.
The nice thing is you can download the issues in any format you like, from jpg, to pdf, and epub.
Bone up on your history of the magazine at wikipedia.