Mayo Clinic is the first and largest integrated group practice in the world. Doctors from every medical specialty work together to care for patients, joined by common systems and a philosophy of "the needs of the patient come first." More than 2,500 physicians and scientists and 42,000 allied health staff work at the original clinic in Rochester, Minn., and newer clinics in Jacksonville, Fla., and Arizona. Collectively, the three clinics treat more than half a million people each year.