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.This year marks 30 years since the construct of family boundary ambiguity (BA) was first introduced in a published article (Boss, 1977) to the interdisciplinary field of family stress. Since that time, the concept of family BA has been widely used by scholars, clinicians, and educators to study and intervene with families experiencing a wide range of stressor situations. However, despite the widespread use of the construct, little has been done to systematically document the research literature pertaining to family BA. This article presents such a review.We approached the task of reviewing the family BA literature with two intertwined purposes. First, we bring together a comprehensive, interdisciplinary review of published research studies using the concept of BA. We address three primary questions: (a) what is the current state of BA theory and how has it evolved over the past 30 years?, (b) what are the domains of study in which the concept of BA has been applied?, and (c) how is BA being operationalized and measured in this research? Our findings to these questions are presented in a descriptive fashion and comprise the main sections of this article (i.e., theory, research, measurement). In addition to cataloging the broad scholarly literature addressing BA, a second purpose of this project was to evaluate the current state of BA research and to identify future directions for a second generation of scholarship in this area. In the final section of the paper, we discuss several implications from our review for carrying BA research forward for another 30 years.