Asthma is a chronic inflammatory disorder of the airways. While the local infiltration of eosinophils and mast cells, and their role in the disease have long been recognized, neutrophil infiltration has also been assessed in many clinical studies. In these studies, airway neutrophilia was associated with asthma severity. Importantly, neutrophilia also correlates with asthma that is refractory to corticosteroids, the mainstay of asthma treatment. However, it is now increasingly recognized that neutrophils are a heterogeneous population, and a more precise phenotyping of these cells may help delineate different subtypes of asthma. Here, we review current knowledge of the role of neutrophils in asthma and highlight future avenues of research in this field. Airway neutrophilia has been associated with asthma severity and asthma exacerbations; however, neutrophils can also be detected in the airways of both healthy subjects and mild asthmatics. Multiple mediators, including chemokines, cytokines, and lipids, can promote neutrophil recruitment to the airways, and smoking and co-morbidities, such as gastroesophageal reflux and obesity, have shown positive relationships with sputum neutrophil counts. Neutrophils can not only combat infections and kill pathogens, but also have adverse effects on the airways, through the effects of proteases and reactive oxygen species. An improved understanding of neutrophil populations would allow better precision in using neutrophils to define asthma phenotypes.