Carvin (plaintiff) and Britain (defendant) were involved in a same-sex relationship for almost 12 years. About five years after they became romantically involved, Carvin and Britain decided to have a child. A friend donated sperm, and Carvin assisted with the artificial insemination of Britain. L.B. was born as a result. During the first six years of L.B.’s life, Carvin and Britain made parenting decisions together and held themselves out as a family unit. L.B. referred to Carvin and Britain as her mothers. Eventually, Carvin and Britain ended their relationship. Britain restricted Carvin’s contact with L.B. To continue having a relationship with L.B., Carvin filed a petition to establish parentage. The family-court commissioner found that Carvin was only a psychological parent and that Carvin thus lacked standing to claim parentage under the Uniform Parentage Act (UPA). The trial court affirmed the commissioner’s finding, and Carvin appealed the decision. The court of appeals found that Washington law allowed for Carvin to be established as a de facto parent, which is a person who is not the legal parent of a child but may be granted custody rights due to the establishment of a parent-like relationship with the child. Britain appealed.