The term “attachment” is now in common usage and, as the readers of this Special Issue are aware, is referenced in a rapidly increasing variety of contexts involving child custody (McIntosh & Chisholm, 2008). The aim of this article is to provide judges, lawyers, mediators and mental health professionals involved in custody assessment with an overview of the history of the field of attachment and its principal measures, together with a clear description of what the term “attachment” does—and does not—mean to attachment researchers and theoreticians. Implications for normative separations that do not involve custody-related assessment or the intervention of courts or mediators are also considered. With respect to contested custody cases, we consider the use of standardized attachment measures, and note that sufficient validation for most such measures in clinical contexts is still developing. We describe three measures taken from the research literature (the Strange Situation procedure, the Attachment Q-sort and the Adult Attachment Interview), each subjected to meta-analyses and widely regarded as “gold standard” methods in research. These three methods come closest at this point in time to meeting criteria for providing “scientific evidence” regarding an individual's current attachment status. Limitations on widespread use include the need for substantiating meta-analyses on father-child relationships, and further validation across a wider spread of children's ages. We are confident that these restrictions can be solved by new research. In the interim, we argue that increased familiarity with the above measures will assist custody evaluators both in standardizing their assessment procedures and their capacity to gain more from the observational data available to them. Such increased standardization and depth of observation should be highly beneficial to the courts. Related to our endorsement of use of attachment measures in family law matters, we address issues of training, and strongly encourage custody evaluators to attend trainings in the principal methods of the field, and insofar as possible, to become certified in their use. Overall, we endorse the position that attachment theory provides important perspectives not only on the emotional process of divorce itself, but as well on the decisions made for and about the children concerned. Thus, this paper argues that attachment, correctly understood, creates a critical foundation for all professionals working with separated families.