Submarine volcanic eruptions and intrusions construct new oceanic crust and build long chains of volcanic islands and vast submarine plateaus. Magmatic events are a primary agent for the transfer of heat, chemicals, and even microbes from the crust to the ocean, but the processes that control these transfers are poorly understood. The 1980s discovery that mid-ocean ridge eruptions are often associated with brief releases of immense volumes of hot fluids ("event plumes") spurred interest in methods for detecting the onset of eruptions or intrusions and for rapidly organizing seagoing response efforts. Since then, some 35 magmatic events have been recognized and responded to on mid-ocean ridges and at seamounts in both volcanic arc and intraplate settings. Field responses at mid-ocean ridges have found that event plumes occur over a wide range of eruption styles and sizes, and thus may be a common consequence of ridge eruptions. The source(s) of event plume fluids are still debated. Eruptions detected at ridges generally have high effusion rates and short durations (hours to days), whereas field responses at arc volcanic cones have found eruptions with very low effusion rates and durations on the scale of years. New approaches to the study of submarine magmatic events include the development of autonomous vehicles for detection and response, and the establishment of permanent seafloor observatories at likely future eruption sites.