The present invention relates to monobactam compounds of Formula I: and pharmaceutically acceptable salts thereof. The present invention also relates to compositions which comprise a monobactam compound of the invention or a pharmaceutically acceptable salt thereof, and a pharmaceutically acceptable carrier. The invention further relates to methods for treating a bacterial infection comprising administering to the patient a therapeutically effective amount of a compound of the invention, either alone or in combination with a therapeutically effective amount of a second beta-lactam antibiotic.