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.
http://www.sri.com/policy/twin/

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/

The MIT Twins Study Homepage

A long-term study of language development in twins. The goal of the project is to compare language learning in identical and fraternal twins to determine which aspects of language and language learning have a heritable basis.
http://web.mit.edu/jganger/Public/ourhome.html

Millennium Twins

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

Twin Research and Genetic Epidemiology

Located at St Thomas' Hospital, London, UK.
http://www.twin-research.ac.uk/

Twin Research

Newsletter, research information, survey.
http://www.twin-research.com/

International Society for Twin Studies

Events, journal, bylaws, membership information.
http://www.ists.qimr.edu.au/

Australian Twin Registry

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

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

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An unpublished dissertation on twins and studies in homosexuality.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 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

Twins Personality Survey

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