I wonder how many serious and dedicated scuba divers actually continue to put off their natural progression from recreational scuba diving to the more advanced techniques of technical diving? Personally, I delayed that progression for far too long. As a professional underwater photo-journalist who specialises in shipwreck research, however, I find myself being drawn more and more towards deeper and deeper wrecks - if only because these are the wrecks that divers want to know more about.
My first choice in books when commencing that transition to more technical expertise, was this book by John Lippman. A number of people have commented that it is out-of-date - but it is only out-of-date if your own expertise has already progressed beyond the level which this book seeks to teach.
Any diver who is seriously thinking about technical diving but who has yet to make the first move in that direction should read this book. Yes, things have moved on since this book first appeared in 1992 - but that does not make the information inaccurate. It simply allows the modern diver to regard this book as the first step towards an exciting extension of their diving career.
Other books (including other books by this author) will then take that diver even further into the realms and complexities of serious deep technical diving.
NM