<p>The prediction of the interfacial area concentration is critical for one-dimensional gas–liquid two-phase flow analyses because the interfacial area concentration governs the mass, momentum, and energy transfer between gas and liquid in actual engineering situations. Introducing a two-group interfacial area transport equation into computational codes is one of the possible options for predicting the interfacial area concentration in transient and developing two-phase flows. The two-group approach treats bubbles in two groups: group-1 for small bubbles and group-2 for large bubbles. Two-group gas velocity is required to solve the two-group interfacial area transport equation. Thus, a one-group gas momentum equation currently used in two-fluid model-based computational codes should be transformed into a two-group gas momentum equation. However, introducing a two-group drift–flux model enables two-group gas velocity prediction via the one-group gas momentum equation without the current computational code structure. The two-group drift–flux model and void fraction covariance play critical roles in modeling the area-averaged relative velocity between the gas and liquid phases, which is critical in modeling the interfacial drag force. First, the framework used to calculate the two-group interfacial area concentration and area-averaged relative velocity via the two-group drift–flux model is described. Second, the paper provides a state-of-the-art review for two-group drift–flux correlations and void fraction covariance correlations developed for adiabatic and boiling two-phase flows in pipes, annuli, and rod bundles.</p>