The term a-Navigation was introduced as an acronym for autonomous navigation of maritime autonomous surface ships. The term was firstly used during the Autonomous and Remote Navigation Trial Project as an analogue to e-Navigation. a-Navigation refers to ship operation and management in automatic mode with the possibility of human monitoring or use in remote control mode. It shall significantly decrease the human risk factor and increase navigational safety. Several research projects and investigations conducted in different countries moved towards further development in practically applied technologies and engineering solutions. Also, several classification societies, e. g. DNV, Russian Maritime Register of Shipping, China Classification Society, and others developed and issued classification rules and/or regulations on maritime autonomous surface ships and conducted proper risk assessment.