Description: Ocean colonization is the theory and practice of permanent human settlement of oceans. Such settlements may float on the surface of the water, or be secured to the ocean floor, or exist in an intermediate position. EMarine cityE is defined at length at http://parole.aporee.org and the history of such facilities is briefly outlined in EPrototype cities in the seaE by Kaji-oEgrady and Raisbeck (2005). One primary advantage of ocean colonization is the expansion of livable area. In addition, it might offer various other possible benefits such as expanded resource access, novel forms of governance (for instance mini-nations), and new recreational activities for athletic humans. Many lessons learned from ocean colonization will likely prove applicable to near-term future outer space and other-planet colonization efforts. The ocean may prove simpler to colonize than interplanetary space and thus occur first, providing a proving ground for the latter. In particular, the issue of legal sovereignty may bear many similarities between ocean and outer space colonization with space station settlements; adjustments to social life under harsher extra-terrestrail circumstances would apply similarly to the world-ocean and to outer space; and many technologies may have uses in both environments.