Preston's major research interest is in the health of populations. He has written primarily about mortality trends and patterns in large aggregates, including twentieth century mortality transitions and black/white differentials in the United States. Recent research, all of which is collaborative, has focused on the mortality effects of cigarette smoking in developed countries. One paper demonstrates that sex mortality differentials in the US are structured on a cohort rather than a period basis and reflect cohort patterns of cigarette smoking. A forthcoming paper demonstrates how this relationship can be used to project mortality over the next 30 years, with major implications for Social Security trust fund balances. A third paper uses data for fifteen countries for the past 60 years to demonstrate the relationship between lung cancer deaths and deaths from other causes, a relationship that enables improved calculations of deaths attributable to smoking. This paper is being contributed to a National Academy of Sciences committee that he co-chairs that is addressing the question of why US life expectancy lags so far behind the world's leaders. A related project is addressing, in an international context, how well the US health care system is working to reduce deaths from cancer of the prostate and breast. He is also engaged in an effort to estimate the number of excess deaths resulting from the tsunami in Indonesia. Preston also has interests in family and fertility and has recently co-authored a paper on the future of American fertility that will appear in a volume of the National Bureau of Economic Research.