The Dialysis Outcomes and Practice Patterns Study (DOPPS) is a prospective, observational study of the relationships between hemodialysis (HD) patient outcomes and HD treatment practices. The DOPPS began in 1996 in the United States, expanding to France, Germany, Italy, Japan, Spain, and the United Kingdom in 1998-1999, and then to Australia, Belgium, Canada, New Zealand, and Sweden in 2002. More than 300 dialysis units have participated in the DOPPS since 1996, with mortality data collected from nearly 90,000HD patients and detailed longitudinal data from nearly 30,000 HD patients. Large sample size and the large treatment practice variation observed in the DOPPS--given its international scope of participation--provide strong statistical power to investigate many different HD practices. Furthermore, the detailed patient data collected in the DOPPS allow relationships to account for differences in a large number of patient characteristics. More than 55 papers have been published from the DOPPS; here we provide a summary of selected DOPPS findings regarding nutrition, mineral metabolism, anemia management, vascular access, depression, and use of multivitamins and statins.