The Colorado Twin Registry (CTR) is a population-based registry housed at the Institute for Behavioral Genetics, University of Colorado. Recruited subjects' birth years date from 1968. Four samples comprise the CTR: the Community Twin Sample, Infant Twin Sample, Longitudinal Twin Sample, and the Early Reading Development Sample. Criteria for enrollment, recruitment strategies, demographic information and zygosity assignment are explained for each sample. In addition, 8 studies in which CTR twins have participated are highlighted. These include studies of early cognition, early reading ability, executive cognitive function, and vulnerability to substance abuse and antisocial behavior. Goals, measures, and brief results are provided for each study. The development of the CTR is an ongoing and evolving process, and it has proved to be a valuable resource, relatively representative of the population from which it was drawn.