Radiation from natural sources is an inescapable and pervasive aspect of existence on the planet Earth. Approximately 80% of the total radiation stems from natural radioactivity in the ambient radiation background of Earth's Environment. Natural radioactivity can be bifurcated further, for which, terrestrial and cosmogenic radionuclides are responsible. Terrestrial environments consist of naturally occurring radioactive materials (NORMs), constituting the primary source of radiation exposure for humans. Primordial radionuclides, such as 238U, 232Th, 40K, and 235U, originate from nucleosynthesis processes in stars, boasting extraordinarily long half-lives. The susceptibility of living organisms to radiation depends on the naturally occurring gamma-emitting radionuclides in the rock and soil of a specific geographic area. High-energy subatomic particles from space, known as cosmic radiation, continuously bombard Earth's surface. These particles interact with atmospheric nuclei, producing cosmogenic radionuclides (3He, 7Be, 14C, and 22Na) and secondary reaction products. Exposure to cosmic rays increases with higher altitudes. This chapter presents a comprehensive overview of the classification of gamma radiation, with a special focus on terrestrial and cosmic radiations. Efforts are made to shed light on diverse origins, properties, and implications for both terrestrial and cosmic radiations. The information presented in this chapter will be useful in advancing scientific knowledge, ensuring radiation safety, and facilitating technological developments in diverse fields.