Human lungs are populated by several distinct resident and circulating NK cell subsets. Since the lungs represent a site frequently exposed to airborne antigens, viral infections, and cancer development, it is likely that NK cells play a vital role in the local immune response in these settings. Understanding the biology and functional regulation of different NK cell subsets in the lung is therefore essential to comprehend their role in both health and disease. In this chapter, we discuss the biology of NK cells in the fetal and adult human lung, with a particular emphasis on tissue-resident NK cells. Additionally, we review current knowledge of human lung NK cells in context of lung cancer, inflammatory conditions, and respiratory viral infections.