Reviews thinking of scientists concerned with mitigating the threat of hazardous asteroids and comets.This book presents the most recent thinking on the development of a reliable defence against objects that could potentially collide with the Earth. Large asteroids and comets can collide with the Earth with severe consequences and collisions are a random process that could occur at any time. To reduce the threat, it is necessary to understand the orbital motions of potentially hazardous objects, probe their structural and compositional nature to a high level of detail, and measure how they respond to the application of large amounts of energy or momentum.This book presents the most recent thinking on the development of a reliable defence against objects that could potentially collide with the Earth. Large asteroids and comets can collide with the Earth with severe consequences and collisions are a random process that could occur at any time. To reduce the threat, it is necessary to understand the orbital motions of potentially hazardous objects, probe their structural and compositional nature to a high level of detail, and measure how they respond to the application of large amounts of energy or momentum.This book presents the most recent research on the development of a reliable defense against objects that can potentially collide with the Earth. Large asteroids and comets can collide with the Earth causing severe consequences, and collisions are a random process that can occur at any time. To reduce the threat, it is necessary to understand these potentially hazardous objects.Preface; 1. Recent progress in interpreting the nature of the near-Earth object population W. Bottke, A. Morbidelli and R. Jedicke; 2. Earth impactors: orbital characteristics and warning times S. R. Chesley and T. B. Spahr; 3. The role of radar in predicting and preventing asteroid and comet collisions with Earth S. J. Ostro and J. D. Giorgini; 4. Interior structures for asteroids and cometals,