This site is a chapter from a book on geochemistry by Dr. W. M. White that is used in a geochemistry course at Cornell University. The 39-page PDF document discusses the composition and evolution of the mantle and core of the earth, and the geochemical methods used to make these determinations. Additional topics include phase transitions, the primitive mantle, differentiation of the mantle, mantle geochemical reservoirs, and evolution of the depleted upper mantle and mantle plume reservoirs. Problems and figures accompany the text.