Scientists believe that the universe is mostly made up of dark matter, a mysterious substance that is different from the ordinary matter people can touch, smell, see, and interact with. Dark matter cannot be directly observed, but it can be studied by examining its effect on ordinary matter. Simplified explanations of complex scientific concepts and fascinating images will help students understand how physicists employ Kepler’s laws of planetary motion, gravitational lensing, particle colliders, and other theories and tools to learn about dark matter. Informative sidebars explore related timely topics in depth, while a Further Reading section provides several resources for additional study.