Interleukin-15 (IL-15), natural killer (NK) cells, and NK T (NKT) cells, components of the innate immune system, are known to contribute to defense against pathogens, including viruses. Here we report that IL-15 −/− (NK − and NKT −/+ ) mice and RAG-2 −/− /γ c −/− (NK − and NKT − ) mice that lack all lymphoid cells were very susceptible to vaginal infection with a low dose of herpes simplex virus type 2 (HSV-2). IL-15 −/− and RAG-2 −/− /γ c −/− mice were 100-fold more susceptible and RAG-2 −/− , CD-1 −/− (NKT − ), and gamma interferon (IFN-γ) −/− mice were 10-fold more susceptible to vaginal HSV-2 infection than control C57BL/6 mice. NK and/or NKT cells were the early source of IFN-γ in vaginal secretions following genital HSV-2 infection. This study demonstrates that IL-15 and NK-NKT cells are critical for innate protection against genital HSV-2.