Since its introduction 30 years ago, family boundary ambiguity (BA) has been a widely used construct in family stress research and clinical intervention. In this article, we present a comprehensive and interdisciplinary review of published research studies that have used BA as a primary variable. Our review identified 37 studies investigating BA in 11 topical domains of research (e.g., missing-in-action families, death, divorce, stepfamilies, illness and caregiving, clergy families). We identify theoretical advancements pertaining to the construct and the methods used to measure BA in these studies. Drawing from this review, we discuss the current state of BA scholarship and identify steps that need to be taken to advance BA research in the future.