Radiation is energy that travels in the form of waves or particles. It can be either natural or man-made. Examples of natural radiation include sunlight, cosmic rays, and radioactive decay from naturally occurring elements such as uranium and radon. Man-made radiation includes x-rays, gamma rays, and radiation from nuclear reactors. Radiation can be both beneficial and harmful to living organisms. The effects of radiation depend on the type of radiation, the amount of exposure, and the sensitivity of the organism exposed.