Compared to other caregiving alternatives, adoption is the most stable and permanent type of placement for children in the welfare system. In fact, despite often being associated with significant parenting challenges, most adoptive placements remain stable. It is also true, however, that some adoptions do not achieve this goal and break down temporarily or permanently. Although this phenomenon has attracted considerable attention among researchers, a number of conceptual and methodological difficulties have been encountered. Definition and identification of cases is problematic, hampering a precise quantification of breakdown rate, although there are good reasons to think that the reported figures under-represent the magnitude of the problem. At the same time, there is general consensus that most adoption breakdowns are not the result of a single cause, but rather a consequence of an accumulation of risk factors. Those identified by research refer to three groups: characteristics of the child, of the adoptive parents and the parent-child relationships, and of the adoption support and services. Finally, one of the more interesting aspects of adoption breakdown research lies in the consideration of its policy and practice implications. Better understanding of the incidence, causes, consequences and implications of adoption instability is one of the many ways to help adopted persons, adoptive parents and adoption caseworkers in confronting and overcoming the many challenges they face.