This issue of Otolaryngologic Clinics, guest edited by Drs. Abtin Tabaee and Edward D. McCoul, is devoted to Refractory Chronic Rhinosinusitis. Articles in this issue include: Classification of Chronic Rhinosinusitis: Working Towards Personalized Diagnosis; Bacterial Pathogens and the Microbiome; Biofilm and Osteitis; Refractory Chronic Sinusitis with Polyposis; Aspirin-Exacerbated Respiratory Disease; Systemic and Odontogenic Etiologies in Chronic Rhinosinusitis; Genetic and Immune Dysregulation in Chronic Rhinosinusitis; Office Procedures in Refractory Chronic Rhinosinusitis; Topical Therapies and Stents; Revision Functional Endoscopic Sinus Surgery; Extended Endoscopic and Open Sinus Surgery for Refractory Chronic Rhinosinusitis; and An Algorithm for Comprehensive Evaluation and Management of Refractory Chronic Rhinosinusitis.