Policy-makers generally believe that science and technology can and will play significant roles in improving homeland security. When Congress established the Department of Homeland Security (DHS), through the Homeland Security Act of 2002, it included the Directorate of Science and Technology (S&T) to ensure that the new department had access to science and technology advice and capabilities for research and development (R&D). The S&T Directorate is the primary organisation for R&D in the DHS. It conducts R&D in several DHS laboratories and funds R&D conducted by other government agencies, the Department of Energy national laboratories, academia, and the private sector. Additionally, the directorate supports the development of operational requirements and oversees the operational testing and evaluation of homeland security systems for the DHS. This book provides a brief overview of the S&T Directorate’s mission, organisation, and budgetary structure; a discussion of selected critiques of the S&T Directorate; and an analysis of selected issues facing congressional policy-makers.