Portal hypertension is a major cause of morbidity and mortality in liver cirrhosis. This article provides a background on the most important aspects of the evaluation of portal hypertension in patients with chronic liver diseases, with special attention to the measurement of portal pressure by hepatic vein catheterization. The rationale, technique, applications, costs, and limitations of measurements of the hepatic venous pressure gradient are thoroughly reviewed. Emerging, noninvasive methodologies for the evaluation of the patient with portal hypertension are also discussed.