Parentage is the legal status from which every other family right flows, and it is established in four very different ways that produce very different levels of security. This article explains the marital presumption, the voluntary acknowledgment, the adjudication, and the functional or intended-parent routes, and why the ones that feel most solid are sometimes the least durable. It follows a hypothetical family through a paternity acknowledgment signed in a hospital and a genetic test taken six years later, showing why the answer is often not the one biology suggests. It explains why the law increasingly refuses to let a genetic test undo a parent-child relationship, and what a person who wants to challenge parentage actually has to prove and when. It covers assisted reproduction, surrogacy, and same-sex parents, where the gap between what families do and what records say is widest. It closes with the practical steps that make a parent-child relationship legally secure in every state, not just the one where the child was born.