UPDATE February 2021: Author Jason Sanford has been investigating the situation at Baen’s Bar, the private forum of Baen Books, after hearing that it was being used increasingly to advocate for political violence. You can read his report here. Baen has temporary placed the forum on hiatus in a reaction to this report.
Baen is one of the established publishers of Science Fiction and Fantasy books. They do not need to see any history of publication either. As long as your book is Science Fiction or Fantasy they will consider publishing it.
If you are a genre writer, you have likely read many books that Baen has published and therefore have a good idea of what they are looking for. They are most interested in Science Fiction stories with “powerful plots with solid scientific and philosophical underpinnings are the sine qua non for consideration for science fiction submissions. As for fantasy, any magical system must be both rigorously coherent and integral to the plot, and overall the work must at least strive for originality.”
They prefer to publish books with a clean unobtrusive writing style. They do not specify how much they pay authors, but they are one of the few recommended publishers by the website Predator & Editor, and so they probably pay their writers at or above the market rate.
Baen prefers books to be between 100,000 – 130,000 words in length but they will consider books that are short than that. They prefer to not receive query letters and only ask that your manuscript is accompanied by a synopsis. Baen prefers online submissions through their easy to use submission manager.
It takes them between nine and twelve months to respond to submissions because they receive such a high volume. So keep that in mind when submitting. They also prefer that you submit your work just to them, but if your work is accepted elsewhere they would like to be notified as soon as possible.
To learn more or submit, visit their website here.