The Longitudinal Study of American Youth (LSAY) is a two-cohort longitudinal study of a national sample of approximately 5,000 young adults, now 36 to 39 years of age. The LSAY was launched in the fall of 1987 with national probability samples of 7th and 10th grade students in public schools throughout the United States. Funded by the National Science Foundation (NSF), the LSAY was originally designed to study the factors related to student interest in science and mathematics, the development of skills in those disciplines, the selection of careers, and the development of sufficient scientific literacy to perform citizenship responsibilities in a democratic society. Over the last two decades, the LSAY has continued to monitor these two cohorts of participants, who represent the core of Generation X. Since 2007, LSAY participants have completed annual questionnaires online and on paper, and the focus of the study has shifted to understanding both career patterns and the acquisition of scientific literacy to make sense of emerging issues such as stem cell research or climate change. The first 20 years of LSAY data are available through the Inter-university Consortium for Political and Social Research (ICPSR).