An overview of multiphase flow phenomena is described on the basis of three relations; a relation between an interaction force and time-averaged physical quantities, a relation between an interaction force and the surrounding flow field, and a relation between time-averaged physical quantities and multiphase flow. The three relations used to theoretically derive the parabolic radial distribution of gas holdup for recirculating turbulent flow in a bubble column are in good agreement with experimental data. General applicability of the three relations for a variety of multiphase flows is also discussed.