Model life tables are a key methodological tool for the study of mortality, especially in countries where statistics are incomplete. The tables published by the United Nations in 1982 paved the way for considerable progress in this field. Now that more complete and reliable data are available, the use and interpretation of these tables can be critically assessed. Zhongwei Zhao shows here that mortality in many developing countries is reflected more accurately by the Coale-Demeny tables (expected to represent mortality in the developed countries) than by those of the United Nations and that, conversely, certain United Nations tables closely match the mortality patterns observed in developed countries, for certain periods at least. The author recommends prudence and flexibility in the use of these model life tables during periods of mortality transition, since the application of a single model throughout the observation period may be hazardous when the age structure of mortality is changing. The clarity of the author’ demonstration helps to lift the confusion which sometimes still persists in this area.