Commercial diving is a form of professional diving. Regardless of the specific sector within commercial diving, it demands a skill set far removed from recreational diving. This discipline encompasses the inspection, maintenance, repair, and construction of underwater facilities, including sewage treatment structures and subaquatic hydro installations such as bridges, oil rigs, nuclear power stations, ships, wind turbines, and other artificial constructions. Additionally, natural features like coral reefs fall within the purview of commercial divers. This book covers the entire mandatory theoretical and practical training program for diving specialists. This manual includes diverse topics such as diving physics, offering insights into contemporary decompression tables and guidance on independent calculations of gas breathing mixtures and procedures, anatomy, diving-related illnesses, treatment of diving-related injuries, first aid, and cardiopulmonary resuscitation. The processes of searching and raising sunken objects are described, operation planning, dive logs, records, and commercial diving standards, blueprints, and report writing, mixed-gas diving, as well as industrial and marine safety. Readers will familiarize themselves with essential practical exercises that every diver should master during underwater descents. This book imparts basic knowledge of the principles and structure of diving gear, such as scuba tanks and rebreathers, as well as equipment for underwater welding and cutting, rigging and locksmith tools, specialized suction pumps, and pumps for ground excavation. Information is also provided on the procedures for various underwater works and the operation of specific diving equipment, including high-pressure compressors, hyperbaric chambers, and rescue gear. Basic knowledge of hydrology and subaquatic structures such as dry docks, mooring structures, and dams will be conveyed. Furthermore, the textbook includes a course on physiological aspects affecting a diver's body during immersion and the actions of rescue divers during the provision of first aid. Despite the variations, a common thread in the training system for commercial divers is the certification of commercial divers. To be eligible to work in many countries, divers are required to possess specific certificates and training. In the United States, two primary certificates are essential for work: the Association of Diving Contractors International (ADCI) and the International Marine Contractors Association (IMCA). Commercial divers generally need certification in the country where they work. For example, divers working in Canada will require certification from the Diver Certification Board of Canada (DCBC); those in Australia fall under the jurisdiction of the Australian Diver Accreditation Scheme (ADAS); and in the United Kingdom, certification from the Health and Safety Executive (HSE) is mandatory. The majority of the current demand for commercial diving in the United States is associated with the repair of oil rigs after hurricanes. Another area of increased demand is the sharp rise in inspections and repairs of bridges, dams, and other structures due to flooding. For those willing to pursue a career in commercial diving, the rewards are generous. The initial annual salary for a commercial diver ranges from $40,000 to $60,000, including comprehensive benefits. As a diver gains experience and proves themselves, the salary can grow to $100,000 or $150,000 per year. The book is valuable for both professional divers and apprentice trainees, as it contains materials that provide an understanding of the peculiarities of the diving profession. Gaining information from this textbook on commercial diving today will yield positive results in any international diving school tomorrow.