Over recent years, significant advances have been made in the modelling of the impact dynamics between debris flows and single and dual rigid and flexible barriers. Numerical tools and analytical formulations have been proposed to predict the impact force, runup height, barrier deformation, and overflow and landing dynamics. However, there remains a dearth of well-recognised tools that can be used in routine engineering design practice because their reliability is unclear. On 8 and 9 May 2022, a virtual Class A Prediction Symposium on Debris Flow Impact Forces on Single and Dual Barriers was held to evaluate the reliability of existing design tools and identify areas for improvement to advance the current state of barrier design. The symposium was organised by The Hong Kong University of Science and Technology, Norwegian University of Science and Technology, Institute of Mountain Hazards and Environment of the Chinese Academy of Sciences, and the Geotechnical Engineering Office of the Civil Engineering and Development Department of the HKSAR Government. This paper summarises the existing research on flow-barrier interaction, and details of the symposium, including the prediction cases and results, roundtable discussion, and future research directions.