The Master Key System is a personal development book by Charles F. Haanel.
The book describes many New Thought beliefs such as the law of attraction, creative visualization and man's unity with God, and teaches the importance of truth, harmonious thinking and the ability to concentrate.
The Book that will not only leave you 'feeling' good, but also 'thinking' good. In The Master Key System, presented as a series of twenty-four lessons, delivered to students, Charles Haanel discusses everything from how to feel healthy to how to become wealthy. Using precise logic and a consistent, common-sense frame-work, Haanel shows us how to achieve that what we most desire. 
Used as thus instructed 'The Master Key' will make of the reader a greater, better personality, and equipped with a new power to achieve any worthy personal purpose and a new ability to enjoy life's beauty and wonder.