The book discusses the methodology and experimental setup of Ultrafst Chemical Exchange Spectroscopy in details. Some application examples of the new method are also included. The method has been successfully applied to the study of fast chemical exchange phenomena in liquid solutions at room temperature. The formation and dissociation dynamics of weak intermolecular interactions were monitored in real time with the method. For interaction enthalpies from -0.6 kcal/mol to -3.3 kcal/mol, the dissociation time constants vary from 3 ps to 140 ps. The dissociation rates of the interactions are strongly correlated with their enthalpies. The correlation can be described with an equation similar to the Arrhenius equation. As another example of chemical exchange spectroscopy, the rate of carbon-carbon single bond rotational isomerization of an ethane derivative in a room temperature liquid solution is measured. Based on the experimental results and density functional theory calculations, the time constant for the ethane internal rotational isomerization under the same conditions is estimated to be ~12 ps.