The widespread adoption of microreactors has been hindered by a lack of knowledge regarding rules and parameters needed for their design. This dissertation deals with the investigation of interfacial area and liquid mass transport in microreactors for gas/liquid reactions. Observations of a reduction in conversion occurring when changing from a glass laboratory device to a stainless steel process device motivated investigations into the effect of material and surface properties on the gas/liquid flow and reaction. This work takes a look inside the machined microstructures produced at the Institute for Micro Process Engineering of the Karlsruhe Institute of Technology and investigates the nature of the solid surfaces resulting from the machining process—the surface roughness and the contact angle of the resulting surface. The effect of wettability on gas/liquid flow in microreactors has been investigated in capillaries of various materials. The absorption of carbon dioxide into aqueous solutions of sodium hydroxide has been used to investigate gas/liquid flow and reaction in capillaries and in a microstructured falling film reactor. Under certain limiting assumptions depending upon the exact rates of reaction and transport, values of the interfacial area and liquid mass transport coefficient can be derived from measurements of reaction. This dissertation contributes a small step towards a better understanding of how measurements of the interfacial area and mass transfer coefficient can be performed, demonstrates why the effect of material wettability cannot be ignored, and provides a stronger basis for further work in the development of general correlations describing microstructured gas/liquid reactors.