The different dimensions of parenthood-for example, biological relatedness, child-rearing, co-residence-are disconnected in increasingly many families as the result of upward trends in separation and repartnering. By studying stepparents' claiming (i.e., stepparents perceiving their adult stepchildren as their own), this study provides insight into how people define kinship and adds a new dimension to knowledge about stepfamilies. Using the Ouders en Kinderen in Nederland (OKiN) survey data, this study (a) provides nationally representative estimates of how Dutch stepmothers and -fathers (N = 3,327) perceive their adult stepchildren and (b) shows how the context (i.e., co-residence, duration, timing, marriage) and relations to biological children relate to stepparents' claiming. The more similar the context is to traditional parent-child relations, the more stepparents claim their stepchildren. As opposed to the expectation that relations to one's own biological children would serve as an important reference, having biological children from either a previous or current relationship has little explanatory power.