This review compiles and synthesizes available information on existing mercury monitoring networks, including (i) air monitoring, (ii) human biomonitoring, and (iii) biota monitoring. It also seeks to highlight gaps in the coverage and scope of the monitoring networks, in particular in terms of geographical distribution and institutional organization (global, regional, national and local studies). The report also aims to provide a basis for further coordination and cooperation between the various networks. It is expected that the results presented here will contribute to and guide the ongoing efforts to improve the geographical coverage of global mercury monitoring systems, thus allowing for better assessment, baseline data gathering and evaluation of projects aiming to reduce mercury pollution worldwide. It is important to note that the objective of the report is not to assess the quality of the presented monitoring networks or initiatives. Such evaluation is critical and should be performed as a follow-up action. Furthermore, the authors of the report acknowledge the importance of mercury monitoring efforts in other essential media not included here, such as water and soil. The comprehensive review of the monitoring efforts in those media is therefore elements to be included.