Leukocyte telomere length (LTL) is a biomarker of human aging in that it is relatively short in individuals who display aging-related diseases, principally atherosclerosis. The Bogalusa Heart Study (BHS) has provided unique settings to explore the mechanisms that impact LTL dynamics (LTL and its age-dependent attrition) in young adults. This chapter briefly reviews the background of LTL research and original observations on LTL dynamics and the relations to various indices of cardiovascular aging in the black–white cohort of the BHS. Specifically, the results based on both cross-sectional and longitudinal analyses, black–white difference, and genetic study are summarized. By now, there is a vast and sometimes conflicting literature about the links of LTL with aging and aging-related diseases. The original observations in the BHS were instrumental for the development of a whole new look at what LTL dynamics are all about and in what way they enlighten us about human aging.