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 Byrne's film and book The Secret.

The issue between the old regime and the new, the crux of the social problem, is entirely a question of conviction in the minds of the people as to the nature of the Universe. When they realize that the transcendent force of spirit or mind of the Cosmos is within each individual, it will be possible to frame laws that shall consider the liberties and rights of the many instead of the privileges of the few.

As long as the people regard the Cosmic power as a power non human and alien to humanity, so long will it be comparatively easy for a supposed privileged class to rule by Divine right in spite of every protest of social sentiment. The real interest of democracy is therefore to exalt, emancipate and recognize the divinity of the human spirit.

To recognize that all power is from within. That no human being has any more power than any other human being, except such as may willingly be delegated to him. The old regime would have us believe that the law was superior to the law-makers. Herein is the gist of the social crime of every form of privilege and personal inequality, the institutionalizing of the fatalistic doctrine of Divine election.