Flanagan was born in Bucks County, PA in 1919. He attended the University of Michigan, majoring in English. Worked for Life Magazine as the science editor and in 1947 he left to create a popular science magazine. He eventually created Scientific American, which was first published in May 1948. He served as editor until he retired in 1984.
From the description of Dennis Flanagan papers, 1952-1988. (Cornell University Library). WorldCat record id: 165394063
From the description of Reminiscences of Dennis Flanagan : oral history, 1986. (Columbia University In the City of New York). WorldCat record id: 269253388