This chapter presents an overview of nanosensors and nanotechnology, including nanosensor construction, six basic types of nanosensors, and six prerequisites for the optimum functioning of nanosensors. The chapter discusses the transformation of nanomaterials when exposed to the environment, followed by safety issues involving human exposure and environmental pathways such as lung, dermal, and intestinal ingestion. Finally, nanosensor utilization in the homeland security and infrastructure industries was discussed, which include radiation physics, delayed neutron activation analysis, terahertz imaging, biosensing, and chemical vapors. New instrument standards and test methods and data are also discussed.