Abstract: The Vulnerability Assessment Team (VAT) at Los Alamos National Laboratory believes that physical security can only be optimized through the use of effective vulnerability assessments. As a result of conducting vulnerability assessments on hundreds of different security devices and systems in the last few years, we have identified some of the attributes of effective assessments. These, along with our recommendations and observations about vulnerability assessments, are summarized in this paper. While our work has primarily involved physical security (in contrast to, for example, computer, network, or information security), our experiences may have applicability to other types of security as well.