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I'm looking for some good apocalypse books, hopefully some that are in a series. Thanks

You could try The Passage series by Justin Cronin. There's three books and they introduce some really good sci-fi elements, not to mention the books are extremely well written and immersive.

The 5th wave series by Rick Yancey is pretty good, as is the Maze Runner series by James Dashner. They’re both exciting and fast-paced books from the young adult genre with some great sci-fi and apocalyptic elements.

The Last: A Novel by Hanna Jameson is a murder mystery set among people trapped in an isolated hotel post-apocalypse.