Donor-shared sibling families have recently emerged. Families who conceived using the same anonymous donor are locating one another through websites designed to match children with their biogenetic half-siblings. Based on a survey of 587 parents with donor-conceived children, we discovered that a growing number of unrelated parents whose children are genetically related are organizing into durable groups. These groups mainly exist on the Internet where members can choose their level of participation. A smaller group has met offline, but most select one or two families they especially connect with. Overall, these families illustrate that genetics cannot be ignored. Whereas some respondents view donor-siblings as a latent affiliation--an insurance policy for future questions by their children--others have used the Internet as a social arena to connect and form relationships. In this new world, the Internet is altering how kinship is discovered and formed. (Contains 7 tables, 3 figures and 13 notes.)