Mass transfer is the most important process in multiphase reactors. In many applications in the chemical industry, the mass transfer time determines the operational time of the multiphase reactors. Successfully predicting volumetric liquid-phase mass transfer coefficients under various operating conditions is a challenging task. The effects of various parameters (including pressure and temperature) should be taken into account. The applicability of the classical mass transfer theories to newly proposed chemical reactors needs to be validated. A possible correction should be considered. The effects of turbulence and catalyst particles on the enhancement of mass transfer should be better characterized. Last but not least, the presence of a chemical reaction (especially a complex one) should change the mass transfer conditions and the bubble shape and behavior (in the case of bubbling) in the multiphase reactors, and the process should be well modeled. Multiphase reactors operated with foaming systems (for instance aqueous alcohol solutions), electrolytes (salts), and surface active substances are especially interesting. Manuscripts dealing with these scientific problems are included in this Reprint.