Neutrophils are one of the main types of effector cell in the innate immune system and were first shown to effectively kill microorganisms by phagocytosis more than 100 years ago. Recently, however, it has been found that stimulated neutrophils can also produce extracellular structures called neutrophil extracellular traps (NETs) that capture and kill microorganisms. This Progress article gives an overview of the structure, function and generation of NETs, and their role in infections.