The Longitudinal Study of American Youth (LSAY) is a three-cohort two-generation longitudinal study of national samples of public school students in the United States. The two original cohorts consisted of national probability samples of 7th and 10th grade students selected in 1987. These young adults are now 37 to 40 years of age and reside in all 50 states of the U.S. With continued support from the National Science Foundation, the LSAY will launch a new cohort of 7th grade students in the fall of 2015. The new cohort (called Cohort 3) will be exactly one generation younger than the students in the 1987 cohorts, allowing a generational comparison of changes in American family life, schooling, and society. The original cohorts were 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. Cohort 3 will explore the same questions over the next two decades. The first 20 years of LSAY data are available through the Inter-university Consortium for Political and Social Research (ICPSR).