The detection of materials or devices for nuclear or radiological weapons of mass destruction (NRWMD) is fundamentally important to both homeland security and to military operations. Detection technologies are necessary both to find and to verify the location of materials, components, and systems for NRWMD. They are also central to actions taken after deployment of a NRWMD. The study upon which this report is based was undertaken because of the large and growing importance of detection technologies for NRWMD. While this report will focus on detection of NRWMD, the NRWMD problem does not have a purely technical solution. The reasons for this will become clear in this report. Detectors are necessary but not sufficient for dealing with this problem. This report seeks to be pragmatically comprehensive in its coverage. It takes a level intermediate between policy, on one hand, and technology details, on the other hand. The goal is to provide part of the basis for higher level policy considerations, as well as a framework for lower level, more detailed technical concerns.