Chronic Rhinosinusitis (CRS) is a common disease with a major impact on quality of life. Its etiology is multifactorial and the causal pathology is an inflammation and not an infection. The affected region is the nasal mucosa as well as the mucosa of the sinuses. The symptoms are nasal obstruction, nasal discharge (anterior/post nasal drip), facial pain or pressure and/or olfactory disorder for more than 12 weeks. Beside association to hereditary or systemic diseases, CRS can be divided in chronic local findings (e.g. dental origin, muco- or pyocele, local mycosis, choanal polyp) and general CRS. The latter appears as CRS with nasal polyps or without nasal polyps. According to this, nasal endoscopy combined with investigation for the above mentioned symptoms is essential to diagnose CRS. In order to indicate and plan surgical treatment, CT-scans are necessary. Furthermore, diagnostic tools such as allergy tests, olfactory assessment, laboratory and microbiologic examination, biopsies and tests for aspirin hypersensitivity complete the diagnostic pathway of CRS. The therapeutic approach is local and if necessary oral application of steroids, nasal saline douche and oral long term antibiotics. If this conservative therapy leads to no effect, surgical treatment in terms of functional endoscopic sinus surgery (FESS) has to be considered.