Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Since ancient times ivory, the hard, smooth substance that forms the tusks of elephants and other mammals, such as hippopotamus, walrus or narwhal, has been used for practical and ornamental purposes. However, endangerment of species hunted for ivory has led to restrictions and bans on ivory trade. Despite the restrictions, demand for the material is growing, leading to illegal trade. Learn more about ivory and its trade as well as some of the most spectacular examples of artwork carved from ivory in this book.