Neutrophil extracellular traps (NETs) are intricate structures composed of chromatin, histones, granule proteins, and cytosolic proteins released by neutrophils in response to specific stimuli. NETs play a dual role in both host defense and tissue damage. They are formed through two pathways: suicidal NETosis, which involves NADPH oxidase (NOX), and vital NETosis, which is independent of NOX. NETs exhibit cytotoxic effects against pathogens and host cells, but their excessive activation can lead to severe tissue damage and worsen inflammation. This review aims to elucidate the components of NETs and their impact on host defense, autoimmune diseases, and cancer. NETs consist of DNA and various proteins, including histones, granule proteases, and antimicrobial proteins. The composition of NETs varies depending on the stimulus and disease, with some components playing crucial roles in different pathological states. In host defense, NETs capture and eliminate bacteria, fungi, and viruses. In cancer, NETs promote tumor proliferation, metastasis, and angiogenesis. In autoimmune diseases, NET components act as DAMPs, contributing to organ damage and autoantibody production. Understanding the complex nature of NETs and their components is essential for developing therapeutic strategies in various diseases.Neutrophil extracellular traps (NETs) are intricate structures composed of chromatin, histones, granule proteins, and cytosolic proteins released by neutrophils in response to specific stimuli. NETs play a dual role in both host defense and tissue damage. They are formed through two pathways: suicidal NETosis, which involves NADPH oxidase (NOX), and vital NETosis, which is independent of NOX. NETs exhibit cytotoxic effects against pathogens and host cells, but their excessive activation can lead to severe tissue damage and worsen inflammation. This review aims to elucidate the components of NETs and their impact on host defense, autoimmune diseases, and cancer. NETs consist of DNA and various proteins, including histones, granule proteases, and antimicrobial proteins. The composition of NETs varies depending on the stimulus and disease, with some components playing crucial roles in different pathological states. In host defense, NETs capture and eliminate bacteria, fungi, and viruses. In cancer, NETs promote tumor proliferation, metastasis, and angiogenesis. In autoimmune diseases, NET components act as DAMPs, contributing to organ damage and autoantibody production. Understanding the complex nature of NETs and their components is essential for developing therapeutic strategies in various diseases.