Micro uidics i s g enerally d e ned a s t he s tudy o f uid ow a nd t ransport w here t he i mportant characteristic dimension is between about 100 nm and 100 µm. Although the study of ows that meet this criteria dates back at least hundreds of years, and technologies that knowingly exploit the properties of such ows (e.g., lubrication) are similarly antiquated, the resurgence in research in this area has o ccurred l argely due to t he adv ancements i n m icrofabrication, w hich le d to t he a bility to c onstruct two-dimensional microchannel networks. As a result of this resurgence, when we think about micro uidics now, we think of the well-known technology that evolved from this capability, namely, lab-on-a-chip.