| 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. |
| Sleep Research Study for Twins | | The University of Pennsylvania is recruiting same-sex twins living in the eastern time zone who are between the ages of 25 and 59 to participate in a sleep research study. |
| 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 Studies | | From the Institute of Behavioral Genetics at the University of Colorado. A handful of studies for twins of all ages. |
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