In the Earth's outer radiation belt the flux of energetic electrons and ions can vary significantly over short time periods in response to solar activity. These energetic particles can damage satellites, making it important to be able to understand and predict variability in the radiation belts. In recent years, scientists' understanding of how electrons are accelerated in the radiation belts has changed. Thorne reviews a variety of recent advances in understanding and modeling radiation belt dynamics, highlighting the importance of interactions of energetic particles with magnetosphere waves.