Tectonics (from the Late Latin tectonicus from the Greek τεκτονικός, "pertaining to building") is concerned with the processes which control the structure and properties of the Earth's crust, and its evolution through time. In particular, it describes the processes of mountain building, the growth and behavior of the strong, old cores of continents known as cratons, and the ways in which the relatively rigid plates that comprise the Earth's outer shell interact with each other.