The Elementalists study the primal energies that power nature.  While their obvious interests are studying the effects of the four elements (fire, earth, air, water), their main focus is the Elemental Planes.  These Dimensions exist as pure energy, and Elementalist study where these Dimensions cross over and touch the real world (known usually as the Material Plane) .  The Elementalist believe that where the Elemental and Material Planes touch, pure elements are produced.  For example, the Fire Plane produces fire when it contacts Material matter, whereas the Water Plane produces liquid.  The Elementalists believe that all Material matter is formed by the interaction of these four Planes, and can be controlled by mastering control of Elemental Energy.