Studying the internal structure of our planet as a whole and building a model of the Earth is one of the most important tasks of geophysics. It is this problem that the book of Professor of the University of Sydney K. E. Bullen is devoted to. The book describes methods for constructing Earth models based on theories of elasticity, gravitational potential, seismic wave propagation, and Earth's own vibrations. The history of the issue and modern models calculated using the latest data, including the results of observations with the movement of artificial Earth satellites. At the end of the book, a comparative analysis of the internal structure and composition of the Earth, the Moon and other planets of the solar system is made. The book is designed for geophysicists, astronomers, physicists, specialist geologists and students.