A subject of great interest to Baudouin, Suggestion is shown to compose of a variety of techniques, used in a variety of settings clinical and non-clinical. Baudouin's belief was that suggestion, used responsibly and correctly, could be of great therapeutic benefit to patients suffering from a variety of mental disorders and even physical diseases.

Furthermore, Boudouin was of the opinion that patients could be encouraged to suggest beneficent notions to themselves. Such autosuggestion forms the second half of the book, wherein Boudouin examines ways in which a patient can authoritatively and reliably influence his subconsciousness with autosuggestion, to the enrichment and benefit of his or her life circumstances, outlook, and attainments.

Although the notion of suggestion and autosuggestion as a means of curing or otherwise stymieing disease is both outdated and discredited in the modern day, Boudouin's researches remain a refreshing take on the subject. Operating in the early days of psychology, Boudouin was able to theorize freely without constraint and present an all-embracing, and easily accessible, theory on his subject.

Today Boudouin's ideas are more influential in terms of self-help and character building, than in clinical psychology or psychiatry. However, Boudouin's influence on popular psychologists such as Carl Jung - as well as many self-help authors - would see his ideas passed on to several future generations.