Many times all of us could hear from mass media that an asteroid approached and swept past the Earth. Such an asteroid or comet will inevitably strike the planet some day. This volume considers hazards due to collisions with cosmic objects, particularly in light of recent investigations of impacts by the authors. Each chapter written by an expert contains an overview of an aspect and new findings in the field. The main hazardous effects – cratering, shock, aerial and seismic waves, fires, ejection of dust and soot, tsunami are described and numerically estimated. Numerical simulations of impacts and impact consequences have received much attention in the book. Fairly small impacting objects 50 -100 m in diameter pose a real threat to humanity and their influence on the atmosphere and ionosphere is emphasized. Especially vulnerable are industrially developed areas with dense population, almost all Europe is one of them. Special chapters are devoted to the famous 1908 Tunguska event and new results of its simulations, bolides in the atmosphere and impacts on the early Earth.