The Fundamental Right to Parent and the Policy Supporting Maintenance of Established Parental Relationships: It is has long been established that parents have a fundamental liberty interest in the care, custody, and control of their children. (Troxel v. Granville (2000) 530 U.S. 57.) The courts also recognize that a child's best interests is a core public policy concern that underlies statutory enactments and judicial decisions in this arena. This concept was implicitly recognized in Troxel when the court emphasized there was no allegation that the mother was unfit and that "there is a presumption that fit parents act in the best interests of their children." (Troxel, supra, 530 U.S. at p. 68, italics added.) The state's legitimate interest in the welfare of children has given rise to numerous statutes in a broad array of contexts that seek to ensure a child's well-being while also protecting the liberty interests of parents to raise their children without undue interference by the state or third parties. California statutes have long provided for the use of an evidentiary mechanism--i.e., a presumption--to assist with the determination of parentage when disputes arise concerning the rights and obligations of those charged with, or seeking to be involved in, a parental relationship with a child. The parentage presumption set forth in section 7611(d) of California's Uniform Parentage Act ( 7600 et seq.) is one of these statutes. Under this statutory provision, a person is presumed to be the natural parent of a child if he or she "receives the child into his or her home and openly holds out the child as his or her natural child." ( 7611(d).) The California Supreme Court has concluded that the presumption may be used even though the person is not the biological parent of the child, stating that the "'parentage presumptions are driven, not by biological parentage, but by the state's interest in the welfare of the child and the integrity of the family. .'" (Elisa B. v. Superior Court (2005) 37 Cal.4th 108, 121-122 33 Cal. Rptr. 3d 46, 117 P.3d 660 (Elisa B.); see In re Nicholas H. (2002) 28 Cal.4th 56, 58-59, 63 120 Cal. Rptr. 2d 146, 46 P.3d 932 (Nicholas H.).) The parentage presumption is derived from the "'strong social policy in favor of preserving an ongoing parent and child relationship.'" (Nicholas H., supra, at p. 66.) The presumption is based on the state's interest in "'preserving the integrity of the family and legitimate concern for the welfare of the child. The state has an "'interest in preserving and protecting developed parent-child ... relationships which give young children social and emotional strength and stability.'" ... "'"... A parent who has lived with a child, treating the child as his or her son or daughter, has developed a relationship with the child that should not be lightly dissolved ... ."'"'" (Id. at p. 65.)