Normal polymorphonuclear neutrophil (PMN) function is critical for the maintenance of host-biofilm equilibrium and periodontal tissue homeostasis. Mounting evidence suggests that PMNs play important roles in the control of commensal periodontal flora and initiation of resolution following inflammation caused by accumulating subgingival plaque. Quantitative and qualitative alterations of PMNs in bone marrow, blood, periodontal tissues, and gingival crevicular fluid contribute to host-microbial dysbiosis and onset of irreversible loss of clinical attachment around teeth. Recent findings of specific PMN phenotypes associated with different disease states bring us closer to understanding disease activity and addressing chronic, non-resolved, periodontal inflammation to better monitor and predict patient-specific treatment outcomes. The present review addresses the current state of knowledge in PMN biology in the pathogenesis of periodontal inflammation and the onset of periodontitis.