Leo worked to heal divisions between the church and the modern world. He encouraged the study of both religion and science, especially promoting Thomas Aquinas. He encouraged laypersons to study the Bible for themselves, and endorsed its infallibility. As the first pope of the twentieth century, we have extensive records of him that we lack for other popes, like sound recordings and motion pictures.

Ruling from 1878 to 1903, Leo had the third-longest reign, and was also the oldest pope so far. He died at 93 years old.