The design of a liquid-liquid contact apparatus necessitates the knowledge of fluid dynamics and mass transfer in the dispersion. Since swarm effects and interfacial phenomena induce complex interactions the prediction of process parameters is a challenging task. Single-drop investigations are suited to enable a sophisticated dimensioning based on few simple experiments in combination with published theories and correlations available from literature. This two-part article deals with the fundamentals of fluid dynamics and mass transfer of single droplets and evaluates occurrence and impact of interfacial effects as well as impurities typical for technical applications.