Robotics and Automation in hazardous environments (e.g., fire, radioactivity, underwater) is a research line that still nedds a big amount of research in order to perform the required operations in a safe and reliable manner. Specially, underwater robotics and automation has significant and specific problems to be solved such as networking, data compression, human-robot interfaces, engineering, control systems, and computer science algorithms, among others. This Special Issue focuses on novel scientific solutions to face real robotics and automation problems in underwater scenarios, and also systems that might have application in underwater systems, having obtained results in related environments, such as fire and radiation, among others.