Terahertz (0.1 THz-30 THz) radiation reveals a wealth of information that is relevant for material, biological and medical sciences, with applications that span chemical sensing, high-speed electronics and coherent control of semiconductor quantum bits. To date, there have been no methods capable of controlling THz radiation at molecular scales. Here we report both generation and detection of broadband terahertz field from 10-nm-scale oxide nanojunctions. Frequency components of ultrafast optical radiation are mixed at these nanojunctions, producing broadband THz emission. These same devices detect THz electric fields with comparable spatial resolution. This unprecedented control, on a scale of four orders of magnitude smaller than the diffraction limit, creates a pathway toward THz-bandwidth spectroscopy and control of individual nanoparticles and molecules.