Siddha is one of the oldest system of medicine practiced in India. This system was developed in the state of Tamil Nadu in India. It is supposed to have been conceived by the Siddhas or evolved souls ( numbering 18) who lived in the past. The word 'Siddha' comes from 'Siddhi' which means an object to be attained or perfection of heavenly bliss.
In the Indian tradition, the Siddhas are generally classified into Natha Siddha, Rasa Siddhas, Mahesvara Siddhas, and Sangata Siddhas. the Rasa Siddhas are medicine men, while the Sangata Siddhas are the Buddhist Siddhas. the doctrinal difference among the various groups of Siddhas are minor, and a genuine Siddhas would not mind acquiring initiation into several of these groups. To become a Siddha, sectarian affiliation is unnecessary and irrelevant. Yet it is customary to classify Siddhas into the above groups.
The science of medicine is of fundamental importance to man's well being and his survival, and so it must have originated with man and developed as civilization advanced. It is therefore rather pointless to try to determine the exact point of time when any system of medicine was evolved and codified. A system of medicine is not a discovery but a gradual evolution during successive periods of history. It owes its progress to great men, who have not only enriched the science, but also society and civilization as a whole.