There are 3 books in The Hollow Kingdom Trilogy series.
The Hollow Kingdom Trilogy series does not have a new book coming out soon. The latest book, In the Coils of the Snake (Book 3), was published in October 2005.
The first book in The Hollow Kingdom Trilogy series, The Hollow Kingdom, was published in October 2003.
The Hollow Kingdom Trilogy series primarily falls into the Fantasy genre. This middle grade series was written for ages 8-12, but can be enjoyed by older readers as well.