Marvel Comics revealed plans for a Rogue One comic book series launching in October 2016.
David Gabriel, Senior Vice President of Sales and Marketing, flashed through the panel seen below (photo via Dennis Barger at Wonderworld Comics) during the Diamond Comics Retailer Breakfast this morning at C2E2. He offered no further details on the series, but the slides reveals it to be a 3-issue series plus a One-Shot. UPDATE: ComicBook.com can confirm that the series is a prequel series.
Rogue One: A Star Wars Story doesn't hit theaters until December, so it's safe to assume this won't be an adaptation. The safer bet is that it will be a prequel meant to introduce us to the film's heroes ahead of the theatrical release.