Sensing the terahertz (THz) waves in micro and nanometer regions is key for highly sensitive detection and high resolution imaging. For this purpose, the applications of nanoscale materials and devices are opening doors to new THz sensing and imaging technologies. This chapter gives an overview of nanoscale THz sensors, and then describes highly sensitive and frequency-tunable THz detectors and near-field THz imagers based on carbon nanotubes and semiconductor heterostructures.