Nonalcoholic fatty liver disease (NAFLD), together with metabolic syndrome and obesity, has shown a rapid increase in prevalence worldwide and is emerging as a major cause of chronic liver disease and liver transplantation. Among the various phenotypes of NAFLD, nonalcoholic steatohepatitis (NASH) is highly likely to progress to development of end-stage liver disease and cardiometabolic disease, resulting in liver-related and non-liver–related mortality. Nonetheless, there is no standardized pharmacotherapy against NASH and many drugs are under development in ongoing clinical trials. To develop a successful anti-NASH drug, it is necessary to select an appropriate target population and treatment outcomes depending on whether the mode of action is anti-metabolic, anti-inflammatory or anti-fibrotic. Recently, innovative surrogate markers have been investigated to replace hard outcomes such as liver histology and mortality and reduce the clinical trial duration. Currently, several drugs with fast track designation are being tested in phase III clinical trials, and many other drugs have moved into phase II clinical trials. Both lean NAFLD and typical obese NAFLD have been extensively studied and genetic variants such as PNPLA3 and TM6SF2 have been identified as significant risk factors for lean NAFLD. In the near future, noninvasive biomarkers and effective targeted therapies for NASH and associated fibrosis are required to develop precision medicine and tailored therapy according to various phenotypes of NAFLD.