Although sinusitis is one of the most common problems encountered in clinical practice, it can be a challenge to diagnose and treat appropriately. Sinusitis refers to inflammation (infectious or noninfectious) in the paranasal sinuses. Infectious sinusitis can be bacterial or viral. This article focuses on bacterial sinusitis. Acute bacterial sinusitis usually follows a viral upper respiratory infection (URI) but can also present with severe symptoms 3 to 5 days after onset. Chronic sinusitis has less prominent symptoms and can be easily missed. When antibiotic therapy is warranted, the antibiotic should be chosen based on knowledge of antimicrobial resistance in specific geographic areas and populations. Adjunctive measures include saline irrigation, steam inhalation, nasal and systemic steroids, mucolytics, and decongestants. It is important to identify and treat predisposing factors, including viral URIs, allergic rhinitis, nasal structural abnormalities, gastroesophageal reflux disease, and immune deficiencies.