Synopsis of Paper The Paper is an attempt to suggest a method of estimating the mortality of the future from the records of the past. In Part I., after a brief discussion of the existing methods of calculating rates of mortality, a new method of employing past results called the “cumulative process” is suggested. The chief distinction between the new method and those already in use lies in the fact that an attempt is made to employ existing knowledge of mortality rates when examining new data. It is claimed for the cumulative process that it is suited to a steadily increasing accumulation of knowledge such as should be the result of systematic mortality studies.