Origin of the Earth is an outgrowth of a Lunar and Planetary Institute Conference on the Origin of the Earth. Among the topics covered are theoretical models of the solar nebula, planetary accretion, and models of the differentiation of the Earth into the familiar regimes of hydrosphere, crust, mantle, and core. A central theme of the book is a discussion of the Giant Impact model for the formation of the Moon. This popular model of lunar origin has profound implications for the early history of the Earth, not the least of which is that the Earth must have been in a largely molten state following the Giant Impact. There are samples of the Earth's mantle that show little or no sign of such extensive melting. Is the Giant Impact model incorrect, or have natural processes conspired to erase all traces of its consequences? These and other issues related to the Earth's origin and early differentiation are extensively discussed.