TIM(The Terahertz Intensity Mapper) is a wholly unprecedented experiment to study the cosmic star formation history. It will map a
volume spanning 4.5 billion years of cosmic history (0.52<z<1.67), on scales from 1−50 Mpc (30 arcsec. to ∼ 1 deg. ) using the 158-micron ionized-carbon fine-structure transition. TIM is a balloon-borne imaging spectrometer with two long-slit grating modules combining to cover the 240 to 420 micron regime at a resolving power of 250. New JPL-built sensitive kinetic inductance detector arrays with over 7000 pixels in total enable TIM’s background-limited sensitivity and large throughput. The far-IR band is relatively unexplored, and TIM’s spatial-spectral survey will reveal the 3-D Universe in ionized carbon. The dataset will be analyzed using a new astrophysical technique called line intensity mapping in which the structure of the Universe is studied in the Fourier domain, accessing all forms of emission including the faintest galaxies and diffuse emitters.