There are 5 books in the The Heroes of Olympus series. The newest book is The Blood of Olympus which came out in 2008.

2
The Son of Neptune

Book cover of The Son of Neptune

The SECOND title in this number one, bestselling spin-off series from Percy Jackson creator, Rick Riordan.
This crazy messed up world of gods and monsters is Percy Jackson's reality, which pretty much sucks for him.

Percy Jackson, son of Poseidon, God of the Sea, has woken from a very deep…

4
The House of Hades

Book cover of The House of Hades

The House of Hades is the fourth book in the bestselling Heroes of Olympus series, set in the action-packed world of Percy Jackson.

The stakes have never been higher. If Percy Jackson and Annabeth fail in their quest, there'll be hell on Earth. Literally.

Wandering the deadly realm of Tartarus,…