| Australian Twin Registry: Includes a newsletter, registry for twins, study information and conferences. |
| International Society for Twin Studies: Events, journal, bylaws, membership information. |
| Millennium Twins: A longitudinal sociological study of twins born in the new millennium. |
| Northern California Twin Registry: 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. |
| The Center for Study of Multiple Birth: Recognized internationally as a unique resource for research and information about the causes, effects and problems of multifetal pregnancy. |
| Twin Research: Newsletter, research information, survey. |
| Twin Research: 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. |
| Twin Research and Genetic Epidemiology: Located at St Thomas' Hospital, London, UK. |
| Twin Studies: From the Institute of Behavioral Genetics at the University of Colorado. A handful of studies for twins of all ages. |
| Twin Studies of Homosexuality: An unpublished dissertation on twins and studies in homosexuality. |
| Twins Personality Survey: A twin survey on personality, conducted by researchers at Virginia Commonwealth University. |
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