The other day,
I didn’t know the answer (though I had a pretty good guess), and so I checked with Marvel Comics Editorial Assistant Extraordinaire, Michael Horwitz, who very kindly took the time to give this response:
Currently, Marvel doesn’t accept pitches for original stories, characters, or concepts that haven’t been solicited or asked for by the company. So if you have an idea for a cool new project, for purely legal purposes Marvel can’t look at the idea–just like prose writers are told not to look at fan fiction using their characters. This goes for both new characters you might have created or new stories using existing Marvel characters.
So you’re probably asking, well, then how do I get my written work looked at by Marvel? What Marvel DOES accept are letters of inquiry, which tell us a little about yourself and your writing history. We have a team of people who’ll review the letter of inquiry and if they like what they see, they’ll request a writing sample from you. If you are contacted and asked to produce a story using Marvel characters, then you can pitch that new idea of yours!
I assume that most comic book publishers have the same set of guidelines and standards. It’s hard breaking into this business, though it’s not impossible, either.
By the way, here’s the cover to Issue #5 of NYX (drawn by Alina Urusov), coming out in January.