This theoretical review explores the usefulness of the ambiguous loss framework for understanding the unique and complex realities of boundary-spanning relationships in transnational families. Transnational family processes and interactions are those carried out in both the country of origin and the destination country. We first discuss the distinctive characteristics of ambiguous loss that can impact transnational family experiences in today's globalized world and propose a conceptual model of ambiguous loss in these families. We then describe the factors that affect boundary ambiguity in transnational families and challenges to family reunification, often the long-term goal of families separated by voluntary migration. We conclude by suggesting ways that an ambiguous loss theoretical lens is useful for research and practice with transnational families.