The world’s oceans cover more than 70 percent of the earth’s surface and boast great biological diversity and rich resources, many of which are valuable for human society. Our footprint on the oceans is growing as expanding populations demand more resources and technology makes it ever easier to harvest them. As a result, many of the ocean’s important ecosystems have been seriously degraded. In response over recent decades there have been significant advances in marine conservation policy—the actions and strategies that nations, communities, and individuals adopt to ensure the livelihood of human beings and the marine resources on which they depend. This module synthesizes marine conservation policy development, key principles (e.g., ecosystem management), major stakeholders, significant threats to marine ecosystems, and responses to some of these important issues.