Background: Chronic rhinosinusitis with nasal polyps (CRSwNP) is characterized by IgE hyperproduction and eosinophilic inflammation. The anti-IgE antibody, omalizumab, has demonstrated efficacy in patients with CRSwNP and comorbid asthma previously. Objective: Our aim was to determine omalizumab safety and efficacy in CRSwNP in phase 3 trials (POLYP 1 and POLYP 2). Methods: Adults with CRSwNP with inadequate response to intranasal corticosteroids were randomized (1:1) to omalizumab or placebo and intranasal mometasone for 24 weeks. Coprimary end points included change from baseline to week 24 in Nasal Polyp Score (NPS) and Nasal Congestion Score. Secondary end points included change from baseline to week 24 in Sino-Nasal Outcome Test-22 (SNOT-22) score, University of Pennsylvania Smell Identification Test, sense of smell, postnasal drip, runny nose, and adverse events. Results: Patients in POLYP 1 (n = 138) and POLYP 2 (n = 127) exhibited severe CRSwNP and substantial quality of life impairment evidenced by a mean NPS higher than 6 and SNOT-22 score of approximately 60. Both studies met both the coprimary end points. SNOT-22 score, University of Pennsylvania Smell Identification Test score, sense of smell, postnasal drip, and runny nose were also significantly improved for omalizumab versus placebo. In POLYP 1 and POLYP 2, the mean changes from baseline at week 24 for omalizumab versus placebo were as follows: NPS, -1.08 versus 0.06 (P < .0001) and - 0.90 versus -0.31 (P = .0140); Nasal Congestion Score, -0.89 versus -0.35 (P = .0004) and -0.70 versus -0.20 (P = .0017); and SNOT-22 score, -24.7 versus -8.6 (P < .0001) and -21.6 versus - 6.6 (P < .0001). Adverse events were similar between groups. Conclusion: Omalizumab significantly improved endoscopic, clinical, and patient-reported outcomes in severe CRSwNP with inadequate response to intranasal corticosteroids, and it was well tolerated.