Photoelectrocatalytic (PEC) technologies offer a compelling route towards sustainable solar-to-X conversion, utilising sunlight to drive chemical reactions and produce fuels and valuable chemicals. Unlocking their full potential, however, requires understanding and harnessing phenomena over a vast range of length- and time-scales, from light absorption and charge carrier dynamics at the electronic level to chemical events and mass transport at the macroscopic (device) level. This webinar will showcase the efforts of the PREDICT Consortium towards addressing this challenge, by advancing computational approaches at the electronic, atomistic, mesoscopic, and macroscopic scales, and integrating software implementing these approaches into a holistic multi-scale framework for modelling and simulating PEC materials and processes. Specifically, the webinar will highlight developments in quantum-mechanical modelling of excited states and dynamics, their connection to statistical and kinetic approaches, and their integration with continuum-scale modelling. By connecting phenomena from electrons to devices, PREDICT aims to establish a general-purpose, transferable computational framework that can accelerate innovation in PEC and, more broadly, next-generation solar-to-X technologies.