A comprehensive (742 pages) book on OCaml, covering not only the core language, but also modules, objects and classes, threads and systems programming, interoperability with C, and runtime tools. This book is a translation of a French book published by OReilly.
This book is pretty old...but a nice reading for sure...while I have read more up-to date books on OCaml I feel that by reading this I gain more confidence and knowledge in the language...sometimes reading old books can help us to understand programming languages better...