Areas of overlap between intensification in liquid–liquid systems and membrane technology intensification are highlighted. Liquid membrane systems, supported liquid membranes, pertraction, and application to liquid–liquid coalescence are discussed. Fundamentals of emulsion formation are reviewed, including thermodynamic aspects and the importance of emulsion properties for application. The role of surfactants in emulsion stability is discussed. Characterization of emulsions and predictive methods for emulsion drop size are described. The immobilization of solvents onto hollow fiber membranes is described and the advantages of low solvent inventory and ease of phase separation are highlighted. The basic principle of application of a liquid membrane system is described, showing the generic process steps: emulsification, contact with the feed phase, emulsion breakage, and product recovery. The role of facilitated transport is also described. Different configurations are compared, including hybrid liquid membranes, polymer inclusion membranes, and colloidal liquid aphrons. Selected examples of application of liquid membrane systems are described.