The Earth's Core, Second Edition is a six-chapter book that begins with the general physical properties of the Earth, with emphasis on the core-mantle boundary. This edition discusses the accretion mechanism, heat sources in the early Earth, time of core formation, thermal regime of the Earth, melting-point depth curves, and thermal consequences of iron-alloy core. Subsequent chapters focus on reversals of the Earth's magnetic field; the energetics and the constitution of the Earth's core; and the cores of the Moon and other planets. The role of the Earth's core is vital to the understanding of many geophysical phenomena. It is the seat of the Earth's magnetic field and is responsible as well to some variations in the length of the day.