The American Academy of Otolaryngology—Head and Neck Surgery Foundation has published a supplement to this issue featuring the updated “Clinical Practice Guideline: Adult Sinusitis” as a supplement to Otolaryngology–Head and Neck Surgery. To assist in implementing the guideline recommendations, this article summarizes the rationale, purpose, and key action statements. The 14 developed recommendations address diagnostic accuracy for adult rhinosinusitis, the appropriate use of ancillary tests to confirm diagnosis and guide management (including radiography, nasal endoscopy, computed tomography, and testing for allergy and immune function), and the judicious use of systemic and topical therapy. Emphasis was also placed on identifying multiple chronic conditions that would modify management of rhinosinusitis, including asthma, cystic fibrosis, immunocompromised state, and ciliary dyskinesia. An updated guideline is needed as a result of new clinical trials, new systematic reviews, and the lack of consumer participation in the initial guideline development group.