The Master Key System In Twenty-Four Parts

The Master Key System is a personal development book by Charles F. Haanel (1866–1949) that was originally published as a 24-week correspondence course in 1912, and then in book form in 1916. The ideas it describes and explains come mostly from New Thought philosophy. It was one of the main sources of inspiration for Rhonda Byrnes film and book The Secret (2006).