Mayo Clinic is a nonprofit medical practice and medical research group based in Rochester, Minnesota. It is the first and largest integrated nonprofit medical group practice in the world, employing more than 3,800 physicians and scientists and 50,900 allied health staff. The practice specializes in treating difficult cases through tertiary care. It spends over $500 million a year on research. Dr. William Worrall Mayo settled his family in Rochester, Minn., in 1864 and opened a medical practice that evolved under his sons into Mayo Clinic. Mayo Clinic ranked No. 1 on the 2014-2015 U.S. News & World Report List of “Best Hospitals”, and has been near the top for more than 20 years. It is widely regarded as one of the world’s premier medical practices. The practice is distinguished by integrated care. It has been on the list of America’s “100 Best Companies to Work For” published by Fortune magazine for eight years in a row.