Unconventional gas (including tight, shale, and coal seam gas) production has led to a drastic change of global energy landscape. The fundamental understanding of gas flow behaviours in unconventional gas reservoirs is essential to elevate the potential gas resource recovery. The behaviours of gas flow follow a chain of physicochemical processes in unconventional gas reservoirs, which can be labeled as “coupled processes” implying that one process affects the initiation and progress of another. This process chain is linked together through different disciplines, including geoscience, rock mechanics, multiphase flow, engineering chemistry, and thermodynamics, among others. Although progress on evaluation of migration, control, and recovery of unconventional gas has been achieved using mathematical models and physical experiments, the role of different fluids (eg, CH4 and other hydrocarbons, CO2, and water) in unconventional gas flow is not well understood. Filling this knowledge gap is likely to play a critical impact on raising the potential of unconventional gas resource recovery and on reducing the environmental risks.