Particle radiation is one of the high-risk components of space weather, having the potential to damage sensitive electronics on satellites as well as human tissue on crewed missions. In this talk, I will explain how particle radiation works in the near-Earth space environment and describe two of its main sources: the Sun and the Earth's own magnetosphere. These effects are expected to increase as we approach the next maximum of the solar cycle so NOAA is continuously monitoring and predicting radiation storms.