Amperometric gas sensors have a long and rich history. The present review shows that AGSs are an important member of the electrochemical class of chemical sensors. Many research and development efforts have resulted in practical life-saving sensors, such as the AGS sfor CO, H2S, NO2, O2, or other electrochemically active gases that are now routinely used in industrial hygiene and safety monitoring of people and workplaces. There is an ever-expanding list of analyte targets for the AGS, and its use for electroactive materials like TNT will challenge the sensitivity of the amperometric approach. With the advent of arrays, the AGS is contributing to the detection of a diverse set of complex endpoints including toxicity, cancer detection, and off-odor of materials. New applications such as homeland security and defense against threats have arisen and will challenge the sensitivity and selectivity of the electrochemical technique in general and the amperometric approach specifically. As we demand ever-lower detection levels and since the sensor signal in amperometry is directly proportional to the electrode area, the challenge is to maintain and improve the signal/noise ratio for the analyte. However, the challenge of amperometry is to utilize the ability provided by electronics to detect smaller and smaller amounts of charge/current and to use nanostructures to continue to increase the electrode reactive surface area even with less material used in the electrode. The advancement of MEMS technology and the fast pace of nanotechnology will no doubt enable new AGS designs and materials such that new applications are found for large gas molecules and weakly electroactive gas molecules in applications that will analyze for chemical threats, toxins, food flavors, and fragrances. Much of the modem AGS work focuses on new designs that incorporate microfabrication and nanofabrication to achieve smaller size, low power, lower cost, and portable sensors and sensor arrays with intelligence. New nanormaterials development changes the building blocks that will provide well-organized nanostructures with high surface area, high chemical reactivity at lower temperature, good mechanical strength, and better thermal stability, leading to new catalysts for selectivity, new electrolytes for higher-temperature operation, multiple working electrodes for self-amplifying sensors, and combinations with bioanalytical approaches for biosensors and enzyme-based sensors. MEMS technology and nanotechnology combined with new computational power brighten the future of the AGS and its use within analytical chemistry and especially in field analytical measurements. We now begin a new era of AGS development using new materials, new time-resolved and spatially resolved sensor array approaches, and smaller sensor devices. It is clear that the utility of amperometry will continue and will preserve its place in gas-sensor applications now and in the future and will continue to serve for the betterment of human health, safety, and the environment. © 2008 American Chemical Society.