This book of great use to student and apprentice locksmiths such as myself, as it delves into nearly all the theory and application of knowledge on the subjects of locks, access control and door hardware. Certainly, some of the knowledge is a bit dated, especially on the subject of automobile locks and keying and electronic access control and installation, but that can't be held against the author; lots has changed since the publication date, and even many skilled locksmiths are not fully up to date on that particular subject matter. Also too, this book probably isn't of much use to the intermediate or master locksmith. If you've been working in the field for years, you should know all this stuff. Moreover it should not be used as a substitution for practice, and the author says as much. That said, if you're a beginner, or are training beginners, this should be on your shelf as a reference guide along with your guides of keyways and master keying systems.