Organon der rationellen Heilkunde.

Hahnemann, the founder of homeopathy, embodied his theories in the Organon. The minute doses set down by him did much to correct the evils of the polypharmacy of his time, in which overdosage was pervasive. Hahnemann professed to base medicine on a knowledge of symptoms, regarding investigation of the causes of symptoms as useless; he thus rejected the lessons of pathology. Digital facsimile of the 1810 edition from the Internet Archive at this link. There are several English translations, the first of which was made from the 4th German edition: The Homoeopathic Medical Doctrine, or "Organon of the healing art;" A new system of physic translated from the German of S. Hahnemann by Charles H. Devrient, with notes by Samuel Stratton. Dublin: W. F. Wakeman. 1833. Digital facimile of the 1833 English edition from the Internet Archive at this link.

Digital facsimile of Hahnemann's personal copy of the 5th edition of the Organon (1833) with his autograph revisions for the 6th edition (completed 1842) from UCSF Library at this link. 

"Hahnemann completed his work for the 6th edition in 1842, a year before his death. After Hahnemann’s death in 1843, his widow had a hand-written copy made of Hahnemann’s volume and notes. In 1920, James Ward and William Boericke, American homeopaths based in San Francisco, purchased both the interleaved volume and the manuscript copy. Richard Haehl, a German homeopath, acted as their agent. Haehl used the hand-written copy as the basis for the 6th edition, published in Germany in 1921. The interleaved volume was sent to Boericke in San Francisco, and he used it as the basis of the 1922 English-language edition" (https://www.library.ucsf.edu/archives/homeopathy/digital/).