The discovery and initial description of the interferon-λ (IFN-λ) family in early 2003 opened an exciting new chapter in the field of IFN research. There are 3 IFN-λ genes that encode 3 distinct but highly related proteins denoted IFN-λ1, -λ2, and -λ3. These proteins are also known as interleukin-29 (IL-29), IL-28A, and IL-28B, respectively.