"Space is radioactive". This was the most striking outcome of the early US Explorer space missions of 1958 which revealed belts of energetic charged particles trapped in the Earth's magnetic field. These regions which are named Van Allen Belts after their discoverer, James Van Allen, are the most known, but no t the only source of high energy particles in space. This book gives an overview of the physics of the Earth's environment and of interplanetary space as they interact with energetic particles of solar and galactic origin and describes the methods to asses the impact of radiation on spacecraft and spaceborne electronics. It is intended for Master students of Aerospace Engineering, Physics and Electrical Engineering as well as for engineers and scientists working in the field, designing spacecraft and space equipment susceptible to space radiation.