Different age structures in two populations complicate any comparison of their levels of mortality. Many methods exist which provide death rates or mortality indices adjusted for age and other factors. Such summary measures inevitably lose information, but they are useful for the initial examination of large quantities of data and for the presentation of results. This paper reviews a number of techniques available for producing age-adjusted death rates or mortality indices, emphasizing their historical development. Formulae are given for their calculation. The appropriate context for using each method, and its associated disadvantages are described.