Same-sex couples are becoming parents in increasing numbers through the use of IVF and alternative insemination, and to a lesser degree through surrogacy and adoption. Often these couples form their families using a sperm or egg donor whom they know, and who they have agreed will play an active role in their children’s lives. In these circumstances, children may have more than two people who are their parents. Birth certificates have not kept pace with all these changes in family structures. Although every Australian state and territory allows children with two lesbian mothers to have both mothers registered on their birth certificates, there is no provision allowing for more than two parents to be recorded. This article analyses the purpose of birth certificates, and the domestic and international law relating to these important documents. It also considers what other countries are doing to ensure that children in same-sex families can have all their parents recorded on their birth certificates. It concludes with recommendations about how Australia should modernise its birth certificates to allow for the recording of up to four parents.