This document discusses plate tectonics and the three types of plate boundaries: divergent boundaries, convergent boundaries, and transform boundaries. Divergent boundaries occur where plates move apart, like at mid-ocean ridges, convergent boundaries occur where plates move together and one plate subducts under the other, forming mountain ranges. Transform boundaries occur where plates slide past each other horizontally, like at the San Andreas fault. The document provides examples of each boundary type and discusses how the different interactions between oceanic and continental plates result in volcanism, earthquakes, and mountain building.