Waterborne commerce is increasing rapidly and presenting ports with challenges that could not have been imagined even two decades ago. By 2020, the total volume of cargo shipped by water is expected to be double that of 2001 volumes. At the same time, lifestyle changes have made the cruise industry the fastest growing segment of the travel industry achieving more than 2,100 percent growth since 1970. To accommodate increases in trade volume, increases in the size of cargo and cruise ships, and new security requirements, many U.S. ports are investing billions of dollars in infrastructure improvements such as deeper channels, larger cranes, and other facility and property enhancements. While many of these investments facilitate improvements in the operational efficiency of existing port operations, many ports also need to physically expand to meet business demands. Even the ports that have traditionally viewed themselves as environmental stewards of coastal resources are finding it challenging to balance economic, environmental, and social issues, i.e., to grow sustainably. To ensure that this growth is executed responsibly, many ports have proactively addressed their environmental and related socio-economic responsibilities through the development of Environmental Management Systems (EMSs). The purpose of this primer is to help ports develop EMSs and understand how an EMS can advance port sustainability.