NK cells, originally considered part of innate immunity, now exhibit features of both innate and adaptive immunity. They express a range of activating and inhibitory receptors that help maintain self-tolerance while enabling responses to pathogens and tumors. Unlike traditional innate cells, NK cells can adapt to their environment and even develop antigen-specific memory, blurring the distinction between innate and adaptive immunity. NK cells are not merely cytotoxic but also produce cytokines and chemokines, influencing other immune cells like dendritic cells and macrophages. Their function is regulated by a complex interplay of receptors, including those that detect stress-induced molecules and self-MHC class I molecules. NK cells can become hyporesponsive in the absence of MHC class I signals or in the presence of excessive activating signals, a process known as "tuning." This tuning allows NK cells to respond appropriately to different environmental cues, such as during infection or in steady-state conditions. NK cells also play a role in immunosurveillance and can be manipulated for therapeutic purposes, such as in cancer treatment. Recent studies suggest that NK cells can develop memory-like functions, enabling them to respond more effectively to previously encountered pathogens. These findings challenge the traditional view of NK cells as purely innate and highlight their complex, multifaceted role in the immune system.NK cells, originally considered part of innate immunity, now exhibit features of both innate and adaptive immunity. They express a range of activating and inhibitory receptors that help maintain self-tolerance while enabling responses to pathogens and tumors. Unlike traditional innate cells, NK cells can adapt to their environment and even develop antigen-specific memory, blurring the distinction between innate and adaptive immunity. NK cells are not merely cytotoxic but also produce cytokines and chemokines, influencing other immune cells like dendritic cells and macrophages. Their function is regulated by a complex interplay of receptors, including those that detect stress-induced molecules and self-MHC class I molecules. NK cells can become hyporesponsive in the absence of MHC class I signals or in the presence of excessive activating signals, a process known as "tuning." This tuning allows NK cells to respond appropriately to different environmental cues, such as during infection or in steady-state conditions. NK cells also play a role in immunosurveillance and can be manipulated for therapeutic purposes, such as in cancer treatment. Recent studies suggest that NK cells can develop memory-like functions, enabling them to respond more effectively to previously encountered pathogens. These findings challenge the traditional view of NK cells as purely innate and highlight their complex, multifaceted role in the immune system.