Interferon regulatory factors (IRFs) are critical components of virus-induced immune activation and type I interferon regulation. IRF-3 and IRF-7 are activated in response to a variety of viruses or following engagement of Toll-Like Receptor (TLR) 3 and TLR4 by double stranded RNA (dsRNA) and LPS, respectively. The activation of IRF-5, is much more restricted. Here we show that in contrast to IRF3 and IRF7, IRF5 is not a target of the TLR3 signaling pathway but is activated by TLR7 or TLR8 signaling. We also demonstrate that MyD88, IL-1 receptor associated kinase (IRAK) 1 and TNF-receptor associated factor (TRAF) 6 are required for the activation of IRF-5 and IRF-7 in the TLR7 signaling pathway. Moreover, ectopic expression of IRF-5 enabled type I interferon production in response to TLR7 signaling, while knockdown of IRF-5 by small interfering RNA (siRNA) reduced type I interferon induction in response to the TLR7 ligand, R-848. IRF-5 and IRF-7 therefore emerge from these studies as critical mediators of TLR7 signaling.