In 1948 Josiah Russell published what was a remarkably innovative study in the demographic history of medieval England. It principally involved exploitation of evidence in the Domesday Survey, bishops' registers, an array of manorial extents, the poll taxes and the inquisitions post mortem. Russell's approach displayed a competence in demographic methodology that was unusual, indeed precocious, for a historian of population at this time. The book, one could claim, was unique in an era that pre-dated the formal emergence of historical demography in the 1960s by almost three decades. It revealed a striking willingness to experiment with formal demographic methodology on sources that had never been created with the purpose of recording the flow of vital events or measuring demographic stocks. While over the years its shortcomings have been exposed, it contains much material that is of immense value for medieval English demographic analysis. Its findings continue to be cited and none more so than the estimates Russell made of life expectancy of the tenants-in-chief of the crown based upon the inquisitions post mortem (IPMs). In this chapter the focus will be on Russell's use of the IPMs in the form of a reassessment of his approaches with a view to establishing means of refining estimates of adult life expectancy and the seasonality of mortality from these sources.