Multiphase pipe flows are represented by gas–solid pneumatic transport and solid–liquid slurry transport in pipes, and gas–liquid pipe flows with either gas or liquid as the continuous phase. Fully developed multiphase pipe flows can be characterized by several transport regimes with distinctively different flow patterns and phase interactions dominated by factors such as mass flow ratio of phases, density ratio of phases, pipe orientation relative to gravity direction, transport velocity of continuum phase, and sizes of pipe and particles. Basic topics include the regime classification and flow characteristics in each regime for gas–solid pneumatic transport, solid–liquid slurry transport, and gas–liquid pipe flows, critical transport conditions such as saltation and pickup velocities, mechanisms dominating the pressure drop, suspended flow characteristics in straight pipes and effects of particle loading, electrostatic charges and pipe orientation, characteristics of flow over a bend, such as roping phenomena and bend erosion, and stratified multiphase pipe flow with wavy interfaces.