One of the most tangible examples of Andrew Carnegie's philanthropy is the founding of 2,509 libraries in the late 19th and early 20th centuries throughout the English speaking world, including the United States, United Kingdom, Australia, and New Zealand. Of these libraries, 1,679 of them were built here in the United States. Carnegie spent over $55 million of his wealth on libraries alone and he is often referred to as the "Patron Saint of Libraries."

It is said that Carnegie had two main reasons for donating money to the founding of libraries. First, he believed that libraries added to the meritocratic nature of America. Anyone with the desire to learn could educate themselves and be successful in America like he had been. Second, Carnegie believed that immigrants like himself needed to acquire cultural knowledge of America which a library would enable immigrants to do.

Carnegie indicated that it was the first reason that was the most important to him. As a young boy in Pittsburgh working long hours at his job, he had no access to education. However, a retired merchant, Colonel Anderson, had started a small library of 400 books with his personal collection, which he lent on Saturday afternoons to local boys. This is how Carnegie educated himself. Wrote Carnegie of Colonel Anderson's library, "This is but a slight tribute and gives only a faint idea of the depth of gratitude which I feel for what he did for me and my companions. It was from my own early experience that I decided there was no use to which money could be applied so productive of good to boys and girls who have good within them and ability and ambition to develop it, as the founding of a public library in a community...." It is this desire to make reading material available to people at no cost that made Carnegie build libraries all over the world.