It is a massive treatise on ancient Indian medicine. It contains 8 divisions (Astanga Sthanas): Sutra, Nidana, Vimana, Sarira, Endriya, Chikitsa, Kalpa and Siddha-Sthanas. Each division is further divided into numerous chapters. It describes not only the existing knowledge about medicine in all aspects but also the logic and philosophy behind the medical system.

The present manuscript of Charaka Samhita has a long history behind it. It was originally composed by Agnivesa, one of the six students of sage Atreya and embodied the latter's teachings. Charaka is one of the best known and the most popular name, in Ayurvedic medicine. During the 7th, 8th and 9th centuries when Arabic scholarship was at its height, Charaka was a revered authority in the Saracen and Latin worlds of medicine. Between the eleventh and sixteenth centuries, Charaka was referred to as a great medical authority. Charaka may have lived between the second century BC to second century AD.

During the ninth Century AD, 'Charaka Samhita' was again edited and reconstructed by a Kashmiri Pandit named Dridhabala, a resident of Panjore, situated 7 miles north of Srinagar. He added 17 chapters in the section on Therapeutics (Chikitsa-sthana) and also the two complete sections on Pharmaceutics (Kalpa sthana) and success in treatment (siddhi sthana) by collecting his data from various treatises on the Ayurvedic science. The present form which Charaka Samhita has, was given to it by Dridhabala. It was first translated from Sanskrit into English by A.C Kaviratna in 1897.

Charaka Samhita deals elaborately with subjects such as foetal generation and development, anatomy of the human body, function and malfunction of the body depending upon the equilibrium or otherwise of the 3 humours of the body;  Vata, pitta, and Kapha. It describes etiology, classification, pathology, diagnosis, prognosis, treatment of various diseases and the science of rejuvenation of the body. It discusses elaborately the etiology of diseases on the basis of Tridosha theory. It gives a detailed description of the various diseases including those of the eyes, the female genital organs, normal and abnormal deliveries and diseases of children. Charaka's materia- Medica, consists chiefly of Vegetable products though animal and earthy products are also included in it. All these drugs are classified into 50 groups on the basis of their action on the body.

This Vast treatise also gives an idea of the various categories of doctors specializing in different medical subjects, the physicians and their fees, nursing care, centers of medical learning, schools of philosophy such as 'Nyaya' and 'Vaisesika' which formed the fundamental basis of medical theories, medical botany and classification of the animal kingdom, particularly in regard to properties of their flesh etc. It also describes various customs, tradition, legends, routine of daily life, habits of smoking and drinking, dress and clothing of the people of that era.

Commentary on Charaka Samhita by Chakrapanidatta called 'Charaka-tatparya-tika' or 'Ayurveda Dipika' written in the 11th cent AD(1066AD) is very famous. Other commentaries are by Patanjali (not available), Hair Chandras in AD 111 ( not available), Japjjatas 'Nirantar-Pad-Vyakha', Shiva Das's 'Charaka-tattva-Pradipika' and Ganga Dhar's 'Jalpa-Kalpa-taru' in AD 1879.

Susrutha Samhita

This is the main source of knowledge about surgery in ancient India. Susrutha's original version 'Salya Tantra' was later revised  and supplemented by another Susrutha (the younger). It came to be known as 'Susrutha Samhita'. Susrutha's Salya tantra consisted of only 5 divisions. Sutra, nidana, Sarira, Chikitsa and Kalpa. Later additions of 'Uttara Tantra' consisting of 3 divisions called Salyaka (diseases of eye, ear, nose and throat) Bhuta Vidya and Kaumara Bhrtya (diseases peculiar to infants and women ) were done by the younger Susrutha to make 8 divisions in the present 'Susrutha Samhita'.

Susrutha of 'Salya-tantra' was a great surgeon, a teacher of repute and an admirable author. He made great improvements in the general techniques of surgery and performed many new and major operations. He also described a variety of surgical instruments. His technique of dissection is unique, practical and revealing of the structure of the body. His operations for making a new nose or ear lobe of lithotomy, of taking out the dead foetus and abdominal operations are classical marvels.

Of the commentaries on 'Susrutha Samhita', the most renowned is that of Dalhana called 'Nibandha Samgraha' written in the twelfth cent AD. Susrutha Samhita was translated into English in part only by U.C Datta (1883), A Chattopadhyay  (1891), Hoernle (1897). K.L Bhisagaratna transalated it in full between the years 1908 and 1917.

Other Medical Texts

The other Samhitas (medical texts) in Ayurveda are 'Bhela Samhita', Kasyapa Samhita which deals in childrens diseases, 'Astanga Samgraha' and 'Astanga Hridya Samhita' by Vagbhata, 'Chikitsa- Kalika' by Tishtacharya, 'Madhavanidana' or 'Nidana' by Madhavakara, 'Kalyana Karaka' by Ugradilyacharya, a Jain scholar, 'Siddha Yoga' by Vrinda. Vangasena and Chakrapanidatta composed their own treatises on the lines of Vrinda's 'Siddha Yoga', Nadipriksha( Pulse examination) was first mentioned in 'Sarangadhara Samhita' by Sarangadhara.