A two-dimensional computational fluid dynamics study of the two-phase gas-liquid flow in bubble columns is presented. Many of the features of these flows discussed in the literature can be put into a unifying frame by means of the numerical simulations. On the macroscopic scale, the gas-liquid two-phase flow is modelled by a Navier-Stokes system of equations in an Eulerian representation, whereas the motion of the gas is modelled on a smaller scale by tracking individual bubbles or bubble clusters through the liquid in a Lagrangian way. The physical model behind the simulation and typical results obtained in some two-phase gas-liquid flow situations are presented.