A model describing the hydrodynamics and mass transfer of countercurrent liquid-liquid extraction columns is developed and solved. The hydrodynamic model assumes that the dispersed-phase drops behave as spheres of uniform diameter. The model has been found to be qualitatively in agreement;with experimental results published in the literature. It is shown that conventional dispersion interface level control using the;continuous-phase effluent flow rate as the manipulated variable causes unavoidable overshoots and oscillations in the mean holdup and outlet concentrations, while an alternative scheme using the continuous-phase feed flow rate leads to a significant improvement in the dynamic response, A model-based decentralized MIMO control scheme is designed and tested by simulation, and is shown to provide excellent servo and regulatory performance.