*La Vie sous-marine, guide du plongeur naturaliste* is a practical naturalist guide for divers who want to recognize and better understand the marine life they encounter underwater. Written for readers with an interest in observation and field identification, it presents coastal species and habitats in an accessible format suited to diving contexts. The book helps connect underwater sightings with broader ecological patterns, offering guidance on identifying organisms, interpreting their behavior, and appreciating the diversity of marine environments. Its compact, field-oriented approach makes it useful as a companion for dives and as a reference for readers seeking a clearer view of the living underwater world.