A data diode is a unidirectional network device that allows data to travel in only one direction, commonly used in high-security environments like defense, nuclear power plants, and industrial control systems to protect against cyberattacks. Originally developed by governments in the 1980s–1990s as an alternative to air gaps, data diodes have evolved into hardware-software combinations capable of handling multiple protocols simultaneously. They are now widely deployed across sectors including utilities, oil and gas, aviation, and manufacturing, with regulations in the US and Europe increasingly mandating their use for safety-critical systems.