Name : Tomonori TOTANI Institute : NAO.JP E-mail : totani@th.nao.ac.jp TITLE : Very/Extremely High Energy Particles in GRBs: Energy-Loss Processes and Observational Implications ABSTRACT : I will discuss the particle acceleration in GRBs and expected energy loss processes of the high energy particles. Particularly I try to clarify what process becomes important depending on the physical parameters of GRBs, and discuss the implications for the current and future observations. If I have time, I may also give some comments on another topic, that is, the possible background radiation of extremely high-energy neutrinos from structure formation in the universe.