Accurate specification of the particle radiation environment is of crucial importance for mission and spacecraft design with respect to the quantification of radiation effects and the choice of alternative mission architectures. Reliable nowcasting and forecasting of the particle radiation environment is indispensable for our efforts to diagnose the anomalies of space assets and to plan and implement effective mitigation actions. This session solicits papers on recent advances in our understanding of the processes that control the dynamics of the particle radiation environment in geospace and beyond and contribute to its improved specification and forecasting.