Abstract. This paper studies a statistical skin-color model and its adaptation. It is revealed that 1 human skin colors cluster in a small region in a color space; 2 the variance of a skin color cluster can be reduced by intensity normalization, and 3 under a certain lighting condition, a skin-color distribution can be characterized by a multivariate normal distribution in the normalized color space. We then propose an adaptive model to characterize human skin-color distributions for tracking human faces under di erent lighting conditions. The parameters of the model are adapted based on the maximum likelihood criterion. The model has been successfully applied to a real-time face tracker and other applications.