This paper describes the origins and international impact of the Mayo Clinic through 1939. Multispecialty group practice was invented at the clinic a century ago. A visiting Canadian physician wrote in 1906, "Specialization and cooperation, with the best that can be had in each department, is here the motto. Cannot these principles be tried elsewhere?" Mayo Clinic's major (and underappreciated) role in the development of rigorous postgraduate (specialty) training is addressed. Unlike traditional academic medical centers that emphasize research, Mayo's main mission has always been patient care. This activity has been undertaken in an environment enriched by extensive programs devoted to specialty training and clinical research.