There are three states of matter that are common on Earth. These are solids, liquids, and gases. All types of matter (substances) can exist in any one of the three states. Matter changes back and forth from one state to another as heat is added or removed. The most important thing to know about states of matter is that matter is made of tiny pieces called particles. As heat is added or removed from matter, the arrangement, speed, and attraction of the particles changes.