Adaptor proteins are composed exclusively of domains and motifs that mediate molecular interactions, and can thereby link signaling proteins such as activated cell-surface receptors to downstream effectors. Recent data supports the notion that adaptors are not simply coupling devices that hard-wire successive components of signaling pathways. Rather, they display highly dynamic properties that direct the flow of information through signaling networks. The binding activity of adaptors can be regulated by conformational reorganization, and by the cooperative association of domains within the same adaptor. Furthermore, an individual adaptor can deliver different outputs by utilizing distinct combinations of binding partners. Adaptors can also control the oligomerization of receptor signaling complexes, and the subcellular location and duration of signaling events, and act as coincidence detectors to enhance specificity in cellular responses.