Interferons (IFNs) exert their pleiotropic effects through at least two different receptors. IFNs alpha/beta (type I IFNs) crossreact with presumably common receptors, while IFN gamma (type II IFN) initiates its biological effects through its own specific receptor system. Transmembrane proteins corresponding to the ligand binding chains of these receptors have recently been cloned. But transfection experiments revealed that additional components are probably involved in high affinity binding of some type I IFN subtypes and that a species specific putative signal transducer is required to confer biological responsiveness to IFN gamma. Although some elements involved in transcriptional regulation of interferon inducible genes have been identified, the pathways involved in these regulatory processes are not understood as yet. The current knowledge on the structure of IFN receptors is reviewed in the context of some recent advances on other cytokine receptors.