Patients with severe asthma and concomitant chronic rhinosinusitis often have severe, refractory upper and lower airway inflammation. This inflammation has been proposed to be similar throughout the upper and lower airways leading to the unified airways concept. This article reviews chronic rhinosinusitis with and without nasal polyps, and the subgroup with aspirin-exacerbated respiratory disease, while focusing on the relationship with asthma. Additionally, diagnosis and treatment with current and newer therapies are discussed.