: Today, terrestrial Internet can be easily accessed with various types of terminals almost anytime and anywhere on the land. But this is not yet the case in the ocean mainly due to huge differences between terrestrial and marine environments. Although satellite Internet services are available in marine environments, at the time-being, they are neither cost-effective nor popular due to their inherent weaknesses in construction, launching and operation. Ever-increasing human activities in the ocean require marine Internet to provide handy, reliable and cost-effective high-speed Internet access not only on surface but also underwater in marine environments. This is due to the fact that a huge number of sensors and things have been deployed underwater, and this number is still increasing. How to interconnect them becomes an important issue that is necessarily addressed in order to form large and sophisticated underwater systems. This paper discusses the major available network technologie...