This update to GMA 2013 provides the most recent information available for the worldwide emissions to air, releases to water, and transport of mercury in atmospheric and aquatic environments. In this report, “mercury” refers to the chemical element in all forms, in contrast to the Minamata Convention, which distinguishes “mercury” from “mercury compounds.” The report reflects progress made by the scientifi c community, national authorities and organisations in better understanding mercury cycling (Chapter 2), atmospheric mercury emissions (Chapter 3), mercury levels in air (Chapter 4), atmospheric transport and fate (Chapter 5), releases to water (Chapter 6), and the cycling and methylation of mercury in the aquatic environment (Chapter 8). In addition to updating GMA 2013, new sections are included on observed levels of mercury in biota (Chapter 7) and observed levels and trends of mercury in humans (Chapter 9).