The Magisterium Series is a 5-book children's fantasy series. The series is written by Holly Black and Cassandra Clare and is their first collaboration. The series was acquired by Scholastic in April 2012. The first book, The Iron Trial, was published on September 9, 2014, and hit third on the New York Times Middle Grade Bestseller List. The series is set in an underground school where mages train apprentices to control the elements. The books are illustrated by Scott Fischer. The last book, The Golden Tower, was published on September 11, 2018.