Marine shallow-water hydrothermal vents are defined as occurring at less than ~ 200 m below sea level, and are often found off the coasts of island arc volcanoes, which provide the necessary heat source to drive circulation. Recent research suggests that marine shallow-water hydrothermal vents, also known as “shallow-sea” vents (SHVs), are abundant across the Earth. While they have many similarities to deep-sea hydrothermal vents (DHVs), they also have many important differences, primarily due to their occurrence at shallower depths. Here we introduce SHVs and describe some of the processes which influence their geochemistry. This information is summarized from Price and Giovannelli (2017), and is complementary to Giovannelli and Price (2018), which describes the microbiology of shallow-sea vents.