In geology, subduction is the process that takes place at convergent boundaries by which one tectonic plate moves under another tectonic plate, sinking into the Earth's mantle, as the plates converge. These regions are known as "Subduction Zones". A subduction zone is an area on Earth where two tectonic plates move towards one another and one slides under the other. Rates of subduction are typically measured in centimeters per year, with the average rate of convergence being approximately 2 to 8 centimeters per year (about the rate a fingernail grows).

Plates can be formed from either oceanic lithosphere or continental lithosphere. Stable subduction zones involve an oceanic plate sliding beneath either a continental plate or another oceanic plate (that is, the subducted plate is always oceanic while the subducting plate may or may not be oceanic). Subduction zones are often noted for their high rates of volcanism, earthquakes, and mountain building. Continental collision results where a continental plate is subducted.