Superionic phases, characterized by liquid-like ionic mobility within a solid lattice, represent an emerging state of matter in planetary interiors. More broadly, ionic transport processes, including superionic conduction, proton diffusion, and ionic conduction in solids and melts, play a fundamental role in controlling the physical and chemical evolution of Earth and other planets. In Earth, these processes influence electrical and thermal transport, rheology, and deep interior dynamics, while in ice and gas giants, phases such as superionic H2O are thought to modulate magnetic field morphology and thermal evolution. This session brings together experimental, computational, and observational studies of ion transport under extreme pressure–temperature conditions. We welcome contributions on phase relations, transport properties and mechanisms of ionic conduction in solids and melts. High-pressure experiments, first-principles simulations, and geophysical observations are encouraged. This session aims to advance our understanding of ionic transport and superionicity as a unifying process in planetary science.