Surrogacy is one of the most significant assisted reproductive technologies of the modern era, raising novel questions within the realms of Imami jurisprudence and Iranian law. A fundamental question concerns the determination of the child's maternal lineage, as three distinct roles can be identified in this process: the genetic mother (egg provider), the gestational mother (the woman carrying the fetus), and—in some instances—the intended mother (the woman who, by prior agreement and intent, assumes the maternal role). Distinctions between these roles carry significant implications for inheritance, *mahramiyyat* (kinship prohibiting marriage), custody, maintenance, birth registration, and the child's identity. Although Imami jurisprudence lacks a singular, explicit stance on surrogacy, an analysis of the concepts of lineage and birth, alongside customary practices and the child's best interests, indicates that maternal lineage cannot be determined solely based on the act of gestation. Similarly, while Iranian law includes the "Act on Embryo Donation to Infertile Couples," it lacks a clear, independent provision regarding the determination of the mother in surrogacy arrangements. Consequently, determining maternal lineage requires reconciling Sharia principles, jurisprudential rules, contractual terms, and the child's best interests. Adopting a descriptive-analytical approach, this study demonstrates that in the prevailing surrogacy model, the genetic criterion offers a stronger basis for establishing maternity; however, the gestational mother's role in fostering physical and emotional bonds with the child is undeniable and warrants consideration through contractual obligations and legal protections. Therefore, it is recommended that the Iranian legislature enact specific regulations to explicitly define the status of lineage, birth registration, and the consequential legal effects of such agreements.