In this book, we have discussed the important minerals and rocks that constitute our planet, how they form, and where they occur. We have also discussed their use as ore minerals, building materials, and sources of energy. However, Earth materials affect us in a more direct and personal way through our health. Our bodies, like those of all other living organisms, have evolved to use Earth materials for their construction and function. In this chapter, we briefly examine which Earth materials are important for good health and which can cause chemical and physical threats to our well-being. We have room to touch on only a few highlights of this extremely important field. To underline its importance, we can point out that organizations, such as the U.S. Geological Survey, the British Geological Survey, and the French Geological Survey have divisions devoted to health and the environment and medical geology, and all have Web sites geared to providing important related information to the public (see “Online Resources” at the end of the chapter).