The 12 distinct subtypes that comprise the interferon alpha (IFN?) family of cytokines possess antiviral, anti-proliferative and immunomodulatory activities. They are implicated in the etiology and progression of many diseases, and also used as therapeutic agents for viral and oncologic disorders. However, a deeper understanding of their role in disease is limited by a lack of tools to evaluate single subtypes at the protein level. Antibodies that selectively inhibit single IFN? subtypes could enable interrogation of each protein in biological samples and could be used for characterization and treatment of disease. Using phage-displayed synthetic antibody libraries, we have conducted selections against 12 human IFN? subtypes to explore our ability to obtain fine-specificity antibodies that recognize and antagonize the biological signals induced by a single IFN? subtype. For the first time, we have isolated antibodies that specifically recognize individual IFN? subtypes (IFN?2a/b, IFN?6, IFN?8b and IFN?16) with high affinity that antagonize signaling. Our results show that highly specific antibodies capable of distinguishing between closely related cytokines can be isolated from synthetic libraries and can be used to characterize cytokine abundance and function.