The sea is increasingly being explored for human use. As a result, actors involved in governing maritime activities are not necessarily located in the same geographical place and may not even be in direct contact, but they interact through global and transnational institutions or networks. This thesis presents the marine community concept as a new analytical lens for studying environmental governance of maritime activities. A marine community is a community of users and policy makers involved in the governance of a certain maritime activity. Four marine communities in Hammerfest, St. Eustatius, Bonaire and Svalbard are selected based on two distinct marine regions (the Caribbean Netherlands and the European Arctic) and two different maritime activities (cruise tourism and oil & gas activities).