The Center for Study of Multiple Birth  
   A resource for research and information about the causes, effects and problems of multifetal pregnancy.
   http://pubweb.acns.nwu.edu/~lgk395/csmb.html

Facts About Multiples  
   Information on twins, triplets, quadruplets, quintuplets and higher order multiples. Features a database of multiple birth families, statistics, basic information on twinning, world records and information on fakers.
   http://mypage.direct.ca/c/csamson/multiples.html

TwinMajority.org  
   From 2127, most babies will be twins. This site explains why evolution predicts this.
   http://www.twinmajority.org/

The International Twins Association  
   A non-profit, family-oriented organization to promote the spiritual, intellectual, and social welfare of twins and multiples throughout the world.
   http://www.intltwins.org/

Twins by Twins  
   This site is built for all those that want to learn more about twins and is dedicated to those that are twins and proud of it.
   http://www.geocities.com/twins_by_twins

Twins Network  
   A resource for understanding twins and sharing information. Surveys, facts, news, trivia, links.
   http://www.twinsnetwork.com/