The science of underwater diving includes those concepts which are useful for understanding the underwater environment in which diving takes place, and its influence on the diver. It includes aspects of physics, physiology and oceanography. The practice of scientific work while diving is known as Scientific diving. These topics are covered to a greater or lesser extent in diver training programs, on the principle that understanding the concepts may allow the diver to avoid problems and deal with them more effectively when they cannot be avoided.

A basic understanding of the physics of the underwater environment is foundational to the understanding of the short and long term physiological effects on the diver, and the associated hazards of the diving environment and their consequences which are inherent to diving.

Diving physics are the aspects of physics which directly affect the underwater diver and explain the effects that divers and their equipment are subject to underwater which differ from the normal human experience out of water.

These effects are mostly consequences of immersion in water; buoyancy, the hydrostatic pressure of depth, the effects of the pressure on breathing gases and gas spaces in the diver and equipment, the inertial and viscous effects on diver movement, and the heat transfer effects. Other effects are the physical influences of the underwater environment on human sensory perception. An understanding of the physics are useful when considering the physiological effects of diving, the hazards and risks of diving, the working of underwater breathing apparatus, buoyancy control and buoyant lifting.

Other foundational knowledge of physics for diving includes the properties of gases and breathing gas mixtures under variations of absolute pressure and temperature, and the solubility of gases in fluids.

The human physiology of underwater diving is the physiological influences of the underwater environment on human divers, and adaptations to operating underwater, both during breath-hold dives and while breathing at ambient pressure from a suitable breathing gas supply. It, therefore, includes both the physiology of breath-hold diving in humans, and the range of physiological effects generally limited to human ambient pressure divers either freediving or using underwater breathing apparatus. Several factors affect the diver, including immersion, exposure to the water, the limitations of breath-hold endurance, variations in ambient pressure, the effects of breathing gases at raised ambient pressure, effects caused by the use of breathing apparatus, and sensory impairment. All of these may affect diver performance and safety.

Immersion affects fluid balance, circulation and work of breathing. Exposure to cold water can result in the harmful cold shock response, the helpful diving reflex and excessive loss of body heat. Breath-hold duration is limited by oxygen reserves, and the risk of hypoxic blackout, which has a high associated risk of drowning.

Large or sudden changes in ambient pressure have the potential for injury known as barotrauma. Breathing under pressure involves several effects. Metabolically inactive gases are absorbed by the tissues and may have narcotic or other undesirable effects, and must be released slowly to avoid the formation of bubbles during decompression. Metabolically active gases have a greater effect in proportion to their concentration, which is proportional to their partial pressure, which for contaminants is increased in proportion to absolute ambient pressure.