The Amazing Secrets of the Yogi. c.1937
A Book About You. 1928.
The Master Key System. 1912
Mental Chemistry. 1922.
The New Psychology. 1924.

Haanel's book The Master Key System, was published in 1912, when he was 46 years old. It is written in the form of a course in New Thought, mental development, financial success, and personal health. The book was heavily promoted in the pages of Elizabeth Towne's New Thought magazine The Nautilus. By 1933 it had allegedly sold over 200,000 copies worldwide. Haanel practiced the financial principles he preached, and was a self made success who owned several major companies. According to Stevens, writing in 1909, "He was president of the Continental Commercial Company, president of the Sacramento Valley Improvement Company, and president of the Mexico Gold & Silver Mining Company."

The original Master Key System contained 24 parts or modules of study. The allegedly "lost" chapters of the Master Key System, chapters 25-28, which are found in some editions, are not original, but have been copied from the chapters 11-14 of A book about You. Among the key points of Haanel's system are what he refers to as the laws of concentration, attraction, and harmonious thinking and action. Unique to the Master Key System is a set of exercises that accompany each chapter, and which are systematically building upon each other - they are what makes the Master Key System a system. Another important aspect of the Master Key System is the element of "Truth". The understanding of "Truth" is derived from the understanding that Spirit is all there is, and that it cannot be other than perfect. Truth provides readers/students with certainty, courage and determination to change their life for the better.

In addition to the Master Key System, Haanel wrote several other books including Mental Chemistry, published in 1922, The New Psychology, published in 1924, A Book about You, published in 1927, and The Amazing Secrets of the Yogi, co-authored with Victor Simon Perera and published in 1937.