Preservation Of Quran
Dr. Shehzad Saleem has also written a very detailed book on this subject after two decades of research: http://www.almawridus.org/bookstore/english/history-of-the-quran-a-critical-study/ A summary of this book is also available: http://www.almawridus.org/bookstore/english/history-of-the-quran-a-concise-study/