 This paper reviews the literature on assays used to measure type I interferon, IFNI, pathway activation, and develops consensus terminology. The authors identified 412 assays, which varied widely in terms of what elements or aspects of IFNI pathway activation they measured and how. They also found that no single assay could be considered the gold standard since some may not be specific for IFNI. Additionally, data on reliability or comparing assays were limited, and feasibility was a challenge for many assays. Finally, the authors developed consensus terminology to improve consistency of reporting. This article was authored by Mary Kay Crow, Lars Romblom, Demetrius T. Boompers and others.