A Phase 3, multinational, multicenter, randomized, double-blind, placebo-controlled study comparing the efficacy of Investigational Product (IP) compared to placebo, in patients with moderate CRSwNP (Chronic Rhinosinusitis with nasal polyps). This will be a 1:1:1 randomization enrolling up to 255 patients without asthma and/or AERD history and up to 255 patients without prior surgery, for a total of 510 randomized patients.

Chronic rhinosinusitis with nasal polyps (CRSwNP) is a condition caused by swollen spaces inside thenose and the air-filled spaces in the head (sinuses). Nasal polyps are soft and noncancerous growthsinside of the nose or sinuses caused by swelling. People with CRSwNP often have thick mucus in their nose and sinuses, causing nasal congestion (including stuffy nose and a feeling of pain or pressure in the face), runny nose, mucus running down the back of the throat, and loss of smell. Available treatments such as corticosteroids (medicines to reduce swelling), antibodies (proteins made in lab: dupilumab, omalizumab, and mepolizumab) and nasal surgery provide relief for a short period of time. CRSwNP may reoccur after treatment. Therefore, there is a need to find other medicines for the treatment of CRSwNP.Lebrikizumab is a new drug being developed for treating people with CRSwNP. Lebrikizumab is an antibody that blocks the action of a specific substance that can trigger the swelling involved in CRSwNP. It is not yet approved for treating CRSwNP. Researchers thought that lebrikizumab may help in reducing the symptoms of CRSwNP.The main purpose of this study is to see how well lebrikizumab works in participants with CRSwNP compared to a placebo. All participants will also receive a background treatment with intranasal mometasone furoate (a medicine to decrease swelling).A total of 510 participants around the world will take part in this study. All participants will be assigned to 1 of the 3 treatment groups by a computer, and each group will have about 170 participants. Participants have a 67% chance of receiving lebrikizumab and a 33% chance of receiving placebo. This study will have the following 4 periods: screening, run-in, treatment and safety follow-up.