This thesis explores which factors influence the feasibility of a simultaneous determination of thermal and mutual diffusivities in homogeneous molecular fluid mixtures by dynamic light scattering (DLS). The focus is primarily on binary fluid mixtures, but certain aspects related to multicomponent mixtures are also discussed. Considering both the theory and the experimental implementation of DLS, selected model systems consisting of methane and propane, as well as binary mixtures of liquids with dissolved gases, are studied in this work, allowing fundamental investigations of different influencing factors. Furthermore, various systems relevant for process and energy technologies are investigated, which often have a technical nature. These include mixtures related to biofuels, electrolytes, liquid organic hydrogen carriers, geological hydrogen storage, natural gas, and polymer melts with dissolved blowing agent. Investigations are conducted across a wide range of thermodynamic states, encompassing temperatures between (280 and 560) K, pressures between (0.030 and 20) MPa, and compositions spanning mole fractions between about (0.002 and 0.995). Besides the main aim, this endeavor not only significantly expands the database of reliable diffusivity data but frequently showcases, for the first time, the applicability of DLS to the respective system. Additionally, a signal attribution strategy is developed, which is universally applicable to any binary fluid mixture.