Chronic rhinosinusitis (CRS) is characterized by mucosal inflammation affecting both the nasal cavity and paranasal sinuses; its causes are potentially numerous, disparate, and frequently overlapping. The more common conditions that are associated with CRS are perennial allergic and nonallergic rhinitis, nasal polyps, and anatomical mechanical obstruction (septum/turbinate issues). Other less common etiologies include inflammation (eg, from superantigens), fungal sinusitis or bacterial sinusitis with or without associated biofilm formation, gastroesophageal reflux, smoke and other environmental exposures, immune deficiencies, genetics, and aspirin-exacerbated respiratory disease. A diagnosis of CRS is strongly suggested by a history of symptoms (eg, congestion and/or fullness; nasal obstruction, blockage, discharge, and/or purulence; discolored postnasal discharge; hyposmia/anosmia; facial pain and/or pressure) and their duration for > 3 months. A definitive diagnosis requires physical evidence of mucosal swelling or discharge appreciated during physical examination coupled with CT imaging if inflammation does not involve the middle meatus or ethmoid bulla. Multivariant causation makes the diagnosis of CRS and selection of treatment complex. Furthermore, various types of health care providers including ear, nose, and throat (ENT) specialists, allergists, primary care physicians, and pulmonologists treat CRS, and each is likely to have a different approach. A structured approach to the diagnosis and management of CRS can help streamline and standardize care no matter where patients present for evaluation and treatment. A 2008 Working Group on CRS in Adults, supported by the American Academy of Otolaryngic Allergy (AAOA), developed a series of algorithms for the differential diagnosis and treatment of CRS in adults, based on the evolving understanding of CRS as an inflammatory disease. The algorithms presented in this paper address an approach for all CRS patients as well as approaches for those with nasal polyps, edema observed on nasal endoscopy, purulence observed on nasal endoscopy, an abnormal history and physical examination, and an abnormal history and normal physical examination.