National Naval Volunteers, a United States Navy reserve force of the World War I period commonly abbreviated "NNV"; see United States Navy Reserve
Norwegian Society for the Conservation of Nature (Norwegian: Norges Naturvernforbund), also known as Friends of the Earth Norway and commonly abbreviated "NNV," the largest Norwegian environmental organization
Number needed to vaccinate, a metric used in the evaluation of vaccines and in the determination of vaccination policy, commonly abbreviated "NNV"