A compendium of optimized methods to measure type I interferon efficacy as an antiproliferative or an antiviral agent. These cutting-edge techniques range from the simple to the highly complex and serve to illuminate the signaling cascades and the activation of enzymatic pathways prompted by interferon. The protocols follow the Methods in Molecular Medicine series format, each offering step-by-step laboratory instructions, an introduction outlining the principle behind the technique, lists of the necessary equipment and reagents, and tips on troubleshooting and avoiding known pitfalls. State-of-the-art and highly practical, Interferon Methods and Protocols offers researchers powerful tools not only to ascertain the functions of IFN-stimulatory gene products, but also to identify additional molecular pathways that will clarify our understanding of the many biological events influenced by IFNs.