Atomically thin two-dimensional (2D) transition metal dichalcogenide (TMDC) materials present a remarkable excitonic systems with exciton binding energy usually one order of magnitude higher than those in typical semiconductor materials. As a result, these materials bear great potential to enable the development novel optical and optoelectronic devices. Here we demonstrate some exotic light-matter interaction properties of 2D TMDC materials that result from the extraordinary strong exciton binding energy. This include: 1) giant gating tunability in the optical refractive index of 2D TMDC materials, in which a tunability > 60% is achieved in the refractive index of 2D TMDC materials by electrical gating with a configuration compatible with CMOS devices; 2) room-temperature condensation, where the gas-like excitons may condense into a liquid-like state, electron-hole liquid (EHL). We will also demonstrate the magneto-optical properties enabled by magnetic TMDC materials.