melanie_bryant I'm just curious how many books are in the Horus Heresy series. I've read a few and I'm interested in reading more, but I don't want to get too far ahead and miss something important.
tinyfrog This is a difficult question to answer, as the Horus Heresy series is still ongoing, and new books are being released regularly. As of right now, there are 50 books in the Horus Heresy series, but this number is subject to change in the future.
neil_stone The Horus Heresy is a series of books written by different authors, so there is no one answer to this question. As of February 2020, there are 57 novels and novellas in the series, as well as numerous spin-off books. You can find a full list of the books in the series here: https://www.blacklibrary.com/all-products/horus-heresy.html
