This article is a comprehensive overview of gas-liquid and liquid-liquid mass transfer in microstructured reactors (MSR). MSR are known to offer high heat and mass transfer rates for two phase systems due to high surface to volume ratio as compared to conventional reactors. The reactions with fast kinetics controlled by mass transfer have been successfully intensified using MSR. The first part of the review deals with the methods of mass transfer characterization. Further, different dimensionless parameters used to analyze mass transfer in MSR are discussed. The literature data with different flow regimes and proposed empirical correlations for both gas-liquid and liquid-liquid systems is also presented. The conventional mass transfer models such as penetration and film theory are analyzed. Finally, the important issues of mass transfer in MSR are summed up. (C) 2011 Elsevier Ltd. All rights reserved.