Our move into the Anthropocene era has meant that human activities in and near the world’s oceans have increased exponentially. This expanding use of the oceans and coasts is creating a changing social-ecological environment. Such changes to the marine environment are driving competition for marine and coastal common resources. This chapter outlines the five key factors creating this increased competition, as identified in an analysis of the 15 conflict case studies. These include: an increasing global population; the need for security of supply of water, food and energy; the economic imperative for the blue economy and blue growth; the failure of institutions to keep up with the pace of environmental change; and the changing environment itself.