Chronic rhinosinusitis (CRS) is a heterogeneous group of inflammatory diseases of the nasal and paranasal cavities either accompanied by polyp formation (CRSwNP) or without polyps (CRSsNP). CRSsNP and CRSwNP are prevalent medical conditions associated with substantial impaired quality of life, reduced workplace productivity, and serious medical treatment costs. Despite recent research evidence that contributes to further unveiling the pathophysiology of these chronic airway conditions, the cause remains poorly understood and appears to be multifactorial. A diverse spectrum of alterations involving histopathology, inflammatory cell and T-cell patterns, remodeling parameters (eg, TGF-β), eicosanoid and IgE production, microorganisms, and epithelial barrier malfunctions is reported in the search to describe the pathogenesis of this heterogeneous group of upper airway diseases. Furthermore, novel evidence indicates considerable heterogeneity within the CRSwNP subgroup determining the risk of comorbid asthma. The characterization of specific disease subgroups is a challenging scientific and clinical task of utmost importance in the development of diagnostic tools and application of individualized treatments. This review focuses on recent evidence that sheds new light on our current knowledge regarding the inflammatory process of CRS to further unravel its pathogenesis.