Mixing is an important process in the chemical industry. Poor mixing can contribute to decreased yields and selectivities. The Handbook of Industrial Mixing estimates that yield losses of 5% are common due to poor mixing. Micromixers offer superior mixing capabilities compared to conventional equipment. Micromixers can mix fluids with a high extent of dispersion and offer shorter lengths of diffusion. Various groups have developed creative devices that mix fluids at the microscale. Although each microdevice can offer excellent mixing, it is often difficult to characterize the exact improvement in mixing offered by a micromixer, or to compare small changes in mixer designs. Characterization of the mixing in microdevices is helpful in developing effective devices and comparing them to existing industrial systems and alternative technologies.