Dynamic Light Scattering (DLS) is a powerful tool for probing soft-matter. The history, equipment, and basic theory of DLS is outlined. Three applications of DLS representing contemporary problems in chemical and biomolecular engineering are presented: polymers, proteins, and liquid crystals. DLS was performed on the polymer poly(ethylene glycol) in aqueous solutions to discern a conformational change from a coil to a helix when dissolved in isobutyric acid and to compare DLS and small angle neutron scattering (SANS) measurements. DLS experiments were conducted on the protein GroEL to determine the aggregation kinetics of the protein in solution. Finally, we observed a phenomenon never before seen associated with the relaxation of fluctuations of anisotropy and concentration fluctuations in a lyotropic chromonic liquid crystal solution of cromolyn. This phenomenon causes a significant increase of the effective relaxation time of the anisotropy fluctuations with an increase of the wave-number of the fluctuations.