If you and your twin are over the age of 18, live in the Bay Area, and are interested in registering, you will be invited to participate in studies and be eligible to receive payment for your participation.

Recognized internationally as a unique resource for research and information about the causes, effects and problems of multifetal pregnancy.

A longitudinal sociological study of twins born in the new millennium.

Located at St Thomas' Hospital, London, UK.

Newsletter, research information, survey.

Events, journal, bylaws, membership information.

Includes a newsletter, registry for twins, study information and conferences.

From the Institute of Behavioral Genetics at the University of Colorado. A handful of studies for twins of all ages.

An unpublished dissertation on twins and studies in homosexuality.

Journal of the International Society for Twin Studies. Topics covered in the journal include behavioral genetics, complex diseases, endocrinology, fetal pathology and other areas of research.