The communication among molecules in a liquid takes place through intermolecular interactions. Molecules talk to each other through dipole moments, quadrupole moments, etc. or sometimes more directly through weak intermolecular bonds, for example, hydrogen bonds. Understanding the structure and dynamics of these intermolecular interactions have proven to be crucial in the quest to obtain a better molecular description of chemical reactivity. If for example, a molecule is vibrationally excited, either as a consequence of a chemical transformation or excitation by a laser, then the molecule will initially relax by intramolecular vibrational relaxation where predominantly the low frequency vibrations are excited. Subsequently, these low frequency modes relax by coupling to the low frequency intermolecular solvent modes. The time scale for these intermolecular interactions is in the range from 0.1 to 10 ps, corresponding to a maximum spectral density at a few THz, thus matching the spectral coverage of THz-time domain spectrometers. This paper will describe recent THz-TDS results on both polar and non-dipolar liquids, in particular emphasizing the relation between result obtained with THz- TDS, depolarized Raman scattering, and OHD-RIKES, and the study of hydrogen bonds in polar liquids and crystals.