Medical diagnostics must function in a wide range of environments: from urban hospitals in developed countries (where cost and simplicity are presently not crucial objectives) to remote settings in developing economies, where little is available in terms of infrastructure (and where low cost and great simplicity are everything). The ‘‘developing economy’’ challenge is one that is now being embraced by the microfluidics community: exactly how does one provide biomedical information when there is no electricity, refrigeration, clean water, or trained medical personnel? Although the challenges of inexpensive, self-contained medical diagnostics are often phrased in terms of medical needs encountered in, say, the rural villages and large urban slums of Africa, practical solutions to these challenges would also be widely useful in many other circumstances: examples of other types of applications that share at least some technical requirements include medical diagnosis in military field operations, detection of diseases of animals and plants, verification of food and water safety, environmental monitoring, analyses for homeland security, and chronic and point-ofcare health monitoring. In each area, specific applications require some combination of simplicity, robustness, and low cost. New methods applicable to one have the potential to be applicable to others. Making diagnostics reliable without the infrastructure usually available in a well-supported academic laboratory (where much of the LoC technology has originated) is more difficult than it seems. The characteristics that must be built into a successful system make a long list, and sometimes seem incompatible; for example: how can unskilled personnel accurately measure the intensity of color in a colorimetric assay? How can one use the reliable, workhorse reagents (e.g., common enzymes and antibodies) of bioanalysis if they are unstable in the environments in which they must be used? Because the list is so long, there will probably be no single, best solution, but rather ingenious solutions for each problem that will then be combined in packages tailored to specific applications.