Originally published as a 24-week correspondence course in 1912, “The Master Key System” is a classic self-help book written by Charles F. Haanel. The main ideas of the book were heavily influenced by the New Thought philosophy, and it was notably a significant source of inspiration for Rhonda Byrne’s film and book “The Secret” (2006). Full of simple advice that has helped millions change their lives for the better, this seminal book will appeal to those looking to reach their full potential and is not to be missed by collectors of vintage literature of this ilk. Charles Francis Haanel 1866–1949) was an American philosopher, author and businessman most famous for his affiliation with the New Thought movement. Other notable works by this author include: “The Amazing Secrets of the Yogi” (1937) and “A Book About You” (1928). Many vintage books such as this are becoming increasingly scarce and expensive. It is with this in mind that we are republishing this volume now in an affordable, modern, high-quality edition complete with an autobiographical essay on Charles F. Haanel by Walter Barlow Stevens.