Motile bacteria seek optimal living habitats by following gradients of attractant and repellent chemicals in their environment. The signaling machinery for these chemotactic behaviors, although assembled from just a few protein components, has extraordinary information-processing capabilities. Escherichia coli, the best-studied model, employs a networked cluster of transmembrane receptors to detect minute chemical stimuli, to integrate multiple and conþicting inputs, and to generate an ampliÞed output signal that controls the cell's þagellar motors. Signal gain arises through cooperative action of chemoreceptors of different types. The signaling teams within a receptor cluster may be built from trimers of receptor dimers that communicate through shared connections to their partner signaling proteins.