This chapter presents several types of terahertz (THz) detectors based on carbon nano tube (CNT) and graphene devices and discusses their future applications to nano-carbon THz imagers. The THz frequency region is located between the microwave region and the visible/near-infrared light region. THz technology nowadays is anticipated to have a strong impact in a wide variety of fields, ranging from basic science such as biochemical spectroscopy, astronomy, and condensed-matter physics to practical areas such as high-speed communication, medicine, agriculture, and security. Progress in nano-electronic devices based on semiconductors and superconductors has led to significant improvement in THz devices—for example, quantum cascade lasers with multiple semiconductor quantum wells, superconductor tunneling junction detectors, superconductor nano-bolometers and coherent emitters with high-temperature superconductors. Among various types of nanomaterials, nano-carbons such as CNTs and graphene are promising candidates for future high-performance THz devices, owing to their unique electronic and optoelectronic properties.