Nuclear or radiological terrorism in the form of uncontrolled radioactive contamination presents a unique challenge in the field of nuclear decontamination. Potential targets require an immediate decontamination response, or mitigation plan to limit the social and economic impact. To date, experience with urban decontamination of building materials - specifically hard, porous, external surfaces - is limited to nuclear weapon fallout and nuclear reactor accidents. Methods are lacking for performing wide-area decontamination in an urban environment so that in all release scenarios the area may be re -occupied without evaluation and/or restriction. Also lacking is experience in developing mitigation strategies, that is, methods of mitigating contamination and its resultant radiation dose in key areas during the immediate aftermath of an event and after lifesaving operations. To date, the tremendous strategy development effort primarily by the European community has focused on the recovery phase, which extends years beyond the release event. In this review, we summarize the methods and data collected over the past 70 years in the field of hard, external surface decontamination of radionuclide contaminations, with emphasis on methods suitable for response to radiological dispersal devices and their potentially unique physico-chemical characteristics. This review concludes that although a tremendous amount of work has been completed primarily by the European Community (EU) and the United Kingdom (UK), the few studies existing on each technique permit only very preliminary estimates of decontamination factors for various building materials and methods and extrapolation of those values for use in environments outside the EU and UK. This data shortage prevents us from developing an effective and detailed mitigation response plan and remediation effort. Perhaps most importantly, while the data available does include valuable information on the practical aspects of performing the various remediation methods including costs, coverage rates, manpower, pitfalls, etc., it lacks the details on lessons learned, best practices, and standard procedures, for instance, that would be required to develop a mitigation strategy. While the urban decontamination problem is difficult and there is much more research to do, the existing literature provides a framework for a response plan. Using this framework, in conjunction with computer modeling and relevant data collection, can lead to development of appropriate plans and exercises that would permit development of a mitigation and remediation response. (C) 2015 Elsevier B.V. All rights reserved.