<p>Allergic rhinitis (AR) and chronic rhinosinusitis (CRS) are among the most common chronic airway diseases. They frequently coexist and share immunopathological mechanisms, but remain under-recognised in clinical practice, especially in India. This review synthesises evidence on their clinical overlap, diagnostic challenges, and the role of allergen testing, with emphasis on the Indian context. A structured review of published literature was performed, including international guidelines and Indian epidemiological studies. Data were analysed to identify key areas of overlap in pathophysiology, diagnostic strategies, and management, and to highlight India-specific challenges. Global prevalence of AR is 10–30% and CRS is 5–12%. Indian studies confirm high disease burden, with sensitisation to dust mites, Parthenium weed, grass pollens, cockroach, and molds being most common. Both AR and CRS are linked by Th2-skewed inflammation, epithelial barrier dysfunction, local IgE production, and microbial dysbiosis. Diagnostic overlap results in frequent under-diagnosis of allergy in CRS (“ghost diagnosis”), compounded by limited use of skin prick testing and serum IgE in India. Management is stepwise: intranasal corticosteroids remain the cornerstone; allergen immunotherapy offers disease-modifying potential but is underutilised; biologics provide benefit in severe, refractory CRS with nasal polyps but remain restricted due to cost. Recognition of the AR–CRS overlap, systematic integration of allergen testing, and region-specific immunotherapy strategies are essential for improving outcomes. In India, expanding diagnostic access, standardising allergen panels, and policy measures to improve availability of immunotherapy and biologics represent key priorities for future practice.</p>