One hundred trillion cells, more than 600 muscles, and over 200 bones—these are parts of the twelve major systems that make up the human body. Technological developments have given us a detailed glimpse within our bodies and led to a greater understanding of how we function. Starting with the integumentary system (that's your skin, nails, and hair) and finishing with the reproductive system, the human body covers everything about you—from the outside to the inside. Award-winning science writer Seymour Simon has teamed up with the Smithsonian Institution on this new book about the greatest wonder of the world: the human body.