The fundamentals of droplet formation and motion are discussed, highlighting the importance to intensification of contactor hydraulic performance and mass transfer kinetics. A detailed review of the relationships dictating drop formation, drop size, and velocity in liquid–liquid systems is included. Dynamic behavior during drop formation and the mode of drop detachment from a nozzle are described. The behavior of single discrete drops in unhindered motion is considered, and then developed into the analysis of swarms of drops in hindered motion and in sprays. Key literature discussing droplet behavior is reviewed, with presentation of correlations for prediction of drop size and velocity in these cases. An overview of drop size correlations for liquid–liquid mixtures in stirred vessels is presented. This is followed by a review of correlations developed for drop size in continuous column contactors of various types. These include the Kühni column, the pulsed Karr column, packed columns, spray columns, and rotating disk columns. Quantitative modeling of dispersion and coalescence in stirred vessels based on a population balance approach is also described.