Zhao, L.R. JACoW Publishing Geneva, Switzerland I base this proposal on paper PHYSICAL REVIEW LETTERS 122, 144801 (2019). The speaker should describe the design and demonstration of a terahertz (THz) oscilloscope for recording time information of an ultrashort electron beam. With such THz oscilloscope, nearly 50-fold longitudinal compression of a relativistic electron beam to about 15 fs (rms) is directly visualized with its arrival time determined with 3 fs accuracy. This technique bridges the gap between streaking of photoelectrons with optical lasers and deflection of relativistic electron beams with radio-frequency deflectors, and should have wide applications in many ultrashort electron-beam-based facilities. The speaker shall report on this work and review the world-wide efforts and progress in this domain.