Many believe that microfluidics has the potential to do for chemistry and biology what the integrated circuit has done for electronics — integrating tremendously complex chemical and biological processes into simple easy-to-use devices that will eventually pervade our lives. While microfluidics has made great progress in the last decade — addressing many of the fundamental questions related to manipulating nanoliter volumes of chemicals and solutions — it still faces some very basic challenges as it moves out of the laboratory and into use. Perhaps most basic is the need for fast, accurate characterization of the size and shape of the microfluidic devices themselves. Conventional imaging and measurement techniques have proven adequate for initial development, but are unable to provide the speed and accuracy needed to support the continued development of microfluidic technologies.