This chapter presents a succinct review of the flow patterns, void fraction, pressure drop, and nonboiling heat transfer phenomenon and recommend some of the well-scrutinized modeling techniques. It provides some illustrative example problems focused on some iterative methods for the determination of void fraction and pressure drop and the use of Reynolds analogy-based and empirical heat transfer correlations for the calculation of nonboiling two-phase heat transfer. The phenomenon of gas-liquid two-phase flow embraces several applications pertinent to oil and gas industry, process engineering, heat exchangers, and cooling of nuclear reactors. Gas-liquid two-phase lows are classified as one-component and two-component two-phase low. The two-component two-phase flow is often referred to as nonboiling two-phase flow and is usually encountered in industrial applications such as artificial lift systems and simultaneous transportation of oil and natural gas from remote extraction locations to the processing units.