Miniaturization of chemical equipment is one of process intensification methods. The main advantage of microstructured chemical equipment originates from the small cross sizes of microchannels (2-3 mm or less, usually less than 1 mm). Thus, the capillary and viscous forces dominate over the inertial and gravitational forces, leading to the formation of structured flows. The microsized reactors, mixers, heat exchangers, extractors, etc., have the following significant advantages: (1) lower mass and heat losses during processing; (2) better temperature control of processes; (3) shorter diffusional paths for molecules and ions; (4) ultimate safety due to a small reaction volume; (5) much higher heat and mass transfer rates as compared to macrolevel devices; and (6) narrow residence time, consequently, better selectivity and yield. This special issue includes several papers in the field of hydrodynamics and heat and mass transfer in two-phase flows in microchannels.