Upper gastrointestinal bleeding from peptic ulcer disease is a common clinical event, resulting in considerable patient morbidity and significant health care costs. Inhibiting gastric acid secretion is a key component in improving clinical outcomes, including reducing rebleeding, transfusion requirements, and surgery. Raising intragastric pH promotes clot stability and reduces the influences of gastric acid and pepsin. Patients with high-risk stigmata for ulcer bleeding (arterial bleeding, nonbleeding visible vessels, and adherent clots) benefit significantly from and should receive high-dose intravenous proton pump inhibitors (PPIs) after successful endoscopic hemostasis. For patients with low-risk stigmata (flat spots or clean ulcer base), oral PPI therapy alone is sufficient. For oozing bleeding (an intermediate risk finding), successful endoscopic hemostasis and oral PPI are recommended. Using intravenous PPIs before endoscopy appears to reduce the frequency of finding high-risk stigmata on later endoscopy, but has not been shown to improve clinical outcomes. High-dose oral PPIs may be as effective as intravenous infusion in achieving positive clinical outcomes, but this has not been documented by randomized studies and its cost-effectiveness is unclear.