The Pennsylvania Longitudinal Study of Parents and Children (PALSPAC) Twin Registry was developed to capture a representative sample of multiple births and their parents in the state of Pennsylvania. The registry has two main efforts. The first began in 2012 through recruitment of adolescents in Pennsylvania schools. The second effort, began in January 2019 in partnership with the Pennsylvania Department of Health to capture the birth cohort of twins born from 2007 to 2017. Study recruitment, sample demographics, focus, and measures are provided, as well as future directions. [The paper was published in "Twin Research and Human Genetics" v22 n6 2019.]