Black Library
The publishing company responsible for releasing fiction set in the Warhammer Fantasy and Warhammer 40,000 universes.
While the Black Library has published good books from good authors, some works are of dubious adherence to canon. Here's what George Mann, Head of Black Library, has to say about this:
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" In further conversation, George emphasized that Black Library’s main objective was to 'tell good stories'. He agreed that some points in certain novels could, perhaps, have benefited from the editor’s red pen (a certain multilaser was mentioned) but was at pains to explain that, just as each hobbyist tends to interpret the background and facts of the Warhammer and 40K worlds differently, so does each author. In essence, each [[::Category:Writers|author]] represents an “alternative” version of the respective worlds. After pressing him further, he explained that only the Studio material (rulebooks, codexes, army books and suchlike) was canonical in that it HAD to be adhered-to in the plots and background of the novels. There was no obligation on authors to adhere to facts and events as spelled out in Black Library work."
The have a regular submissions window so you can submit your work. Fa/tg/uys have, as yet, been unsuccesful, leading to hilarious Nerdrage.
In Warhammer 40,000
In-universe, the Black Library is the repository of the Eldar Empire's collected knowledge of Chaos. It is guarded by the Eldar and hidden in the Webway, because that knowledge could be used for great heresy, although now and then, the Harlequins let someone check out a book if it is important that they know something. Ahriman has attempted to enter the Library for some time now; unfortunately, he has yet to succeed and stir some shit up. Doesn't seem to be guarded that closely, since Inquisitor Jaq Draco could just walk in, steal the Eldar's book of Prophecies and walk away with it.