Electromembrane extraction was introduced in 2006 as a totally new sample preparation concept for the extraction of charged analytes present in aqueous samples. Electromembrane extraction is based on electrokinetic migration of the analytes through a supported liquid membrane and into a μL-volume of acceptor solution under the influence of an external electrical field. To date, electromembrane extraction has mostly been used for the extraction of drug substances, amino acids, and peptides from biological fluids, and for organic micropollutants from environmental samples. Electromembrane extraction has typically been combined with chromatography, mass spectrometry, and electrophoresis for analyte separation and detection. At the moment, close to 125 research papers have been published with focus on electromembrane extraction. Electromembrane extraction is a hybrid technique between electrophoresis and liquid–liquid extraction, and the fundamental principles for mass transfer have only partly been investigated. Thus, although there is great interest in electromembrane extraction, the fundamental principle for mass transfer has to be described in more detail for the scientific acceptance of the concept. This review summarizes recent efforts to describe the fundamentals of mass transfer in electromembrane extraction, and aim to give an up-to-date understanding of the processes involved.