Neutrophils are the most abundant circulating leukocyte type in humans and comprise the host's first line of cellular defense against foreign pathogens invasion. On the other hand, neutrophils are the main mediators of tissue damage induced by acute and chronic inflammation. They were once considered to be short-lived, low transcriptional activity, and terminally differentiated homogeneous leucocytes that failed to return to circulation from tissue. However, more evidence has demonstrated that neutrophils can develop into different sub-populations with phenotypic heterogeneity and functional versatility under physiology and pathological conditions. This review summarizes the phenotypic and functional heterogeneity of neutrophils in sepsis and tumor genesis.