Abstract: The abvent of the ASOG and UNIFAC group-contribution methods for the prediction of activity coefficients approximately 15 years ago was a significant boost to the ability of chemical engineers to model chemical processes. This paper reviews the status and recent progress in the group-contribution approach to predicting liquid-phase activity coefficients.Several different types of liquid mixtures arc considered: non electrolyte mixtures with normal-boiling components; mixtures with dissolved gases; mixtures with polymers; and mixtures including strong electrolytes. It is concluded that in recent years much progress has been made in the development of group-contribution models for the prediction of activity coefficients. It is in addition shown that combining activity coefficient models with equations of state renders the group-contribution approach applicable also to the highpressure region.Due to space limitation, this review emphasizes UNIFAC and related models.