Chronic rhinosinusitis (CRS) is one of the most common diseases in western societies, causing significant morbidity and resulting in great financial cost. Some patients suffer persistent or recurrent symptoms despite receiving optimal medical and surgical treatment. The recent publication of revised diagnostic criteria and management guidelines will assist both clinical research and practice. Multiple theories have been advanced regarding the underlying pathogenesis including allergy, bacterial or fungal infection, genetic predisposition and structural anomalies, but at present the majority of cases are still considered idiopathic. Recent studies have shown that traditional laboratory culture techniques may fail to detect microorganisms growing within biofilms or within host mucosal cells. Both bacteria and fungi possess a number of mechanisms for both the evasion and modulation of host immune responses, including the formation of biofilms and the production of superantigens. Historically, treatments such as antibiotics that had been directed at putative causative agents have often been disappointing. There are, however, a broad range of medical and surgical therapies with proven efficacy available to the treating physician. Endoscopic surgical management is evolving rapidly, and there have been pronounced improvements in outcome and reduction in the risk of complications. Recent advances in the understanding of the pathogenesis of this condition have led to some promising therapeutic developments, particularly in respect to topical treatments. Despite improvements in therapy, CRS remains a challenging condition to manage.