Event sensors implement circuits that capture partial functionality of biological sensors, such as the retina and cochlea. As with their biological counterparts, event sensors are drivers of their own output. That is, they produce dynamically sampled binary events to dynamically changing stimuli. Algorithms and networks that process this form of output representation are still in their infancy, but they show strong promise. This article illustrates the unique form of the data produced by the sensors and demonstrates how the properties of these sensor outputs make them useful for power-efficient, low-latency systems working in real time.