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.
- http://www.uphs.upenn.edu/sleepctr/clinicalresearch/twins.pdf

Twins Personality Survey
- A twin survey on personality, conducted by researchers at Virginia Commonwealth University.
- http://www.outofservice.com/twins/

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.
- http://www.australianacademicpress.com.au/Publications/Journals/Twin_R/TResearch.htm

Twin Studies of Homosexuality
- An unpublished dissertation on twins and studies in homosexuality.
- http://www.dai.ed.ac.uk/homes/timt/papers/twin_studies/

Twin Studies
- From the Institute of Behavioral Genetics at the University of Colorado. A handful of studies for twins of all ages.
- http://ibgwww.colorado.edu/~agross/ibg/twinsites.htm

Australian Twin Registry
- Includes a newsletter, registry for twins, study information and conferences.
- http://www.twins.org.au/

International Society for Twin Studies
- Events, journal, bylaws, membership information.
- http://www.ists.qimr.edu.au/

Twin Research and Genetic Epidemiology
- Located at St Thomas' Hospital, London, UK.
- http://www.twin-research.ac.uk/

Millennium Twins
- A longitudinal sociological study of twins born in the new millennium.
- http://www.millennium-twins.de

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.
- http://www.multiplebirth.com/