Joslin was involved for seven decades in most aspects of diabetes investigation and treatment, save for the fact that he did not discover insulin. Following the Toronto group's blockbuster discovery of insulin in 1921, and the group's disbanding several years later, Joslin became effectively the dean of diabetes mellitus. In the mid-1920s, Joslin, in his mid-50s, took the reins as the world spokesman for the "cause of diabetes." He was the first to advocate for teaching patients to care for their own diabetes, an approach now commonly referred to as DSME or Diabetes Self-Management Education. He is also a recognized pioneer in glucose management, identifying that tight glucose control leads to fewer and less extreme complications.