Fundamentals of Gas-Particle Flow is an edited, updated, and expanded version of a number of lectures presented on the "Gas-Solid Suspensions course organized by the von Karman Institute for Fluid Dynamics. Materials presented in this book are mostly analytical in nature, but some experimental techniques are included. The book focuses on relaxation processes, including the viscous drag of single particles, drag in gas-particles flow, gas-particle heat transfer, equilibrium, and frozen flow. It also discusses the dynamics of single particles, such as particles in an arbitrary flow, in a rotating gas, in a Prandtl-Meyer expansion, and in an oscillating flow. The remaining chapters of the book deal with the thermodynamics of gas-particle mixtures, steady flow through ducts, pressure waves, gas-particle jets, boundary layer, and momentum transfer. The experimental techniques included in this book present the powder feeders, the instrumentation on particle flow rate, velocity, concentration and temperature, and the measurement of the particle drag coefficient in a shock tube.