Microfluidic paper-based analytical devices (microPADs) began as a simple idea with an ambitious goal. The idea was to make microfluidic devices out of paper instead of plas tic or glass. The goal was to develop low-cost and portable paper-based diagnostic devices to improve healthcare in developing countries. Over the past 6 years, many developments have been made in the emerging field of paper-based microfluidic devices. Reviewing the develop ment of these devices in the Whitesides group at Harvard University (Cambridge, MA, USA) can provide some insight into the future of the field and encourage scientists from a variety of backgrounds to contribute their expertise toward further development of useful microPADs.