In 2010 the 200th anniversary of the Organon is celebrated by the homeopathic community. Samuel Hahnemann’s Organon of Rational Therapeutics, published in 1810, however, marks neither the beginning of homeopathy nor the endpoint of its development. On the one hand, its contents are based on terms and concepts developed and published by Hahnemann during the preceding two decades. On the other hand, the five revised editions of the Organon that followed in the next three decades contain major changes of theory and conceptions. Hahnemann’s basic idea, running through all the stages of the foundation, elaboration, and defence of his doctrine, may be detected by a comparative review of his works from a historical and philosophical perspective.