The Birth Of Purgatory
The book is very informative and touches many important issues on the development of purgatory. It is also fairly easy to read and keeps you focused on the book. It can be read from beginning to the end but also serves as a great book for looking up facts concerning purgatory and history of the Early Church to the medieval Catholic Church.
The author being French sometimes narrows history down to France and French theologians but generally all of the western church is considered in his investigation.
If you look for protestant views on purgatory it is recommended that you look for additional literature.
