- 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.
- 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. [PDF]
- 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 - 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 - Newsletter, research information, survey.
- 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.
- Twins Personality Survey - A twin survey on personality, conducted by researchers at Virginia Commonwealth University.
