Mechanical and electrical systems are well-known and widely used for environmental control. Thermostatically-controlled air conditioning is a common terrestrial example. In space and undersea situations, constraints such as remoteness (limited or zero resupply), lack of gravity, and a hostile exterior atmosphere provide a challenge to environmental control technology. In particular, the development of environmental systems for future long-duration manned space missions is leading to new and sophisticated applications of chemical and electrochemical processes to augment the basic mechanical/electrical systems. This paper highlights the role of electrochemical processes in spacecraft environmental systems development and, by example, describes the fundamentals of these processes. In overview, oxygen recovery, carbon dioxide removal, two-gas pressure and composition control, water and waste management, and night orbit power supply are shown to be functions which can be at least partially performed with electrochemical processes. Oxygen and nitrogen generation by the electrolysis of water and hydrazine, and electrolytic treatment of urine are described as example processes.