Hepatopulmonary syndrome (HPS) is a pulmonary complication of liver cirrhosis that causes an oxygenation defect. Many patients are asymptomatic at diagnosis or may have non-specific symptoms such as dyspnea. Since the diagnostic criteria of HPS have been established, its prevalence has been better estimated. HPS is an important prognostic indicator for patients undergoing evaluation for liver transplant. Implementation of the Model for End-stage Liver Disease exception policy, has improved the outcomes of HPS, however the mortality remains high. Here we discuss the pathophysiology diagnostic criteria, and the recent experimental studies in HPS.