Time trends in population health risks, whether manifest in risk factors or morbidity and mortality, are an essential challenge to manage in public health. This chapter discusses the assessment and prediction of time trends in health risks, environmental factors driving the time trends, early life environmental exposures with lag time effects, epigenetics as biological memory of early life environmental exposures, birth cohorts, age, and period effects in time trends in health risks, early life epigenetic signatures as predictors of later time trends in health risks, time trends among twin pairs characterizing the time trends, investigative requirements for the twin studies, gene-environment interactions possibly implicating epigenetics, current feasibility limitations in investigations and modifications of epigenetic. While time trend studies in epigenetics have not been carried out yet, the potentials and the challenges are emerging and should inspire future research elucidating causes, correlates, and consequences of epigenetically related traits.