In 1983, he founded his own publishing house, Baen Books, specializing in the adventure, fantasy, military science fiction, and space opera genres.

[1] In late 1999, he started an electronic publishing business called Webscriptions (since renamed to Baen Ebooks), which is considered to be the first profitable e-book vendor.

He left his stepfather's home at the age of 17 and lived on the streets for several months before joining the United States Army; he served in Bavaria.

After stints at City College of New York and as the manager of a folk music coffee shop (a "basket house") in Greenwich Village in the 1960s, he started his publishing career in the complaints department of Ace Books.

While at Galaxy (which absorbed If from 1975) he largely revitalised it, publishing such authors as Jerry Pournelle, Charles Sheffield, Joanna Russ, Spider Robinson, Algis Budrys, and John Varley, and was nominated for several Hugo Awards.

[3] Robert A. Heinlein dedicated his 1985 novel The Cat Who Walks Through Walls to Baen and eight of the other members of the Citizens' Advisory Council on National Space Policy.

In 1983, he had the opportunity to start his own independent company, Baen Books, distributed then and now by Pocket Books/Simon & Schuster; this was possible in part thanks to release from a long-term contract by his good friend Doherty.

Baen Books has grown steadily since and established a large readership among fans of accessible adventure SF, publishing books by authors such as David Weber, John Ringo, Eric Flint, David Drake, Lois McMaster Bujold, Elizabeth Moon, Mercedes Lackey, Larry Niven, and many more.

(Lois Bujold, Eric Flint, John Ringo, and Dave Weber were all Baen discoveries whom Jim promoted to stardom.)

The week before his stroke, Jim bought a first novel from a writer whom Baen Books had been grooming through short stories over the past year.

These innovations earned him respect in the technological community, and increasing disbelief in the publishing trade with perhaps the best comment of all – others began to mimic him, or place e-titles with Webscriptions themselves.

This is a fair description of Jim's life in SF: he was always his own man, always a maverick, and often brilliantly successful because he didn't listen to what other people thought.

[8] Another result of such interaction is that the barflies, the customers frequenting the site, actually talked Jim Baen into charging more for the e-book variation on the publishing trades' advance reading copy — (sampler packages of five books) the house was offering called e-ARCs ("Advanced Reader Copies", emphasis on benefit to the "Reader").

With the interest shown in Flint's 1632 series, he set up a second talk forum for the new writer, one specialized to the buzz of 1632-verse called 1632 Tech Manual.

After concerns over trademark infringement with Dell Magazines (publisher of Analog Science Fiction and Fact, which was originally titled Astounding Stories), it was renamed Jim Baen's Universe.

The magazine, edited by Eric Flint, published its first issue in June 2006, authors contracted including David Drake and Timothy Zahn.

In August 2009, Baen's Universe announced that they would be closing down the magazine due to financial issues, stating "we were simply never able to get and retain enough subscribers to put us on a sales plateau that would allow us to continue publishing".