This chapter discusses rhinosinusitis which is a group of disorders characterized by inflammation of the mucosa of the nose and the paranasal sinuses. Ostial obstruction is the result of chronic rhino-sinusitis. Chronic rhinosinusitis may be caused by multiple factors such as persistent infection caused by biofilms and osteitis, allergy and other disorders of immunity, intrinsic factors of the upper airway, superantigens from Staphylococcus aureus in chronic rhinosinusitis (CRS) with nasal polyps, and colonizing fungi that induce and sustain eosinophilic inflammation. Rhinosinusitis are classified as major and minor symptoms, where major symptoms include nasal obstruction, nasal discharge, hyposmia, facial congestion and facial pain, and minor symptoms include fever, halitosis, headache, cough, fatigue, dental pain and ear pain. Acute rhinosinusitis is caused by the presence of bacteria within the sinus cavity whose ostium is obstructed. Pathological changes of CRS are edema, loss of submucosal glands, ulceration, loss of cilia, fibroplasias, bone remodeling and later changes of goblet cell formation.