Natural killer (NK) cells are a type of cytotoxic lymphocyte that plays a critical role in the immune response against virus-infected cells and cancer cells. NK cell function refers to the ability of these cells to identify and eliminate target cells without the need for prior sensitization or activation. NK cell function is regulated by a complex interplay of activating and inhibitory receptors on the surface of the cell, which allows them to distinguish between healthy cells and abnormal cells. Research in NK cell function aims to understand the molecular mechanisms that control NK cell activation and function, as well as to explore potential therapeutic interventions to enhance NK cell activity in cancer and infectious diseases. This research area is important for developing new immunotherapies that harness the power of NK cells to target and kill cancer cells. Additionally, studying NK cell function can provide insights into immune responses to viral infections and other diseases.