Ashtadhyayi is an oldest known grammar of Sanskrit language. In 400 BC, Dakshiputra Panini, an ancient Sanskrit grammarian, formulated various semantics and syntax, which served as rules for Sanskrit grammar, known as Ashtadhyayi, which literally means eight chapters. Along with the immediate works of forerunners like Nighantu, Nirukta, Pratishakyas, Panini`s Ashtadhyayi is probably the earliest documented works on Sanskrit and over all descriptive linguistics.

Panini, whose work was mainly based on lexicography and grammar, lived during the late Vedic period. Numerous ecological and cultural facts can be inferred and obtained from the terminology that is used in Ashtadhyayi. There are also implications of religion and dharma and the mention of the deity Vasudeva. Panini`s Ashtadhyayi is the most intricate and complex. It is a concise and complete work of grammar on classical Sanskrit that is even superior to any other similar works on other languages. Various inputs from the lexical works in Ganapatha and Dhatupatha have been obtained in order to explain rules and algorithms that are applied to generate appropriate words and language. Ashtadhyayi is exceedingly mechanical, scientific and systematic and the concepts of morpheme and phoneme are intrinsic in its approach, which provide support in explaining the morphology of Sanskrit, without being redundant. With the use of a complex set of lexicon, morphology and syntax, a mechanical meta-language has been used by Panini, which are properly organised by a set of rules. The technical rules and system is considered a milestone in earliest and contemporary linguistics.

The Ashtadhyayi is segregated into eight separate chapters which consist of almost 3,959 rules or sutras. Each chapter is again divided into four segments, known as Padas.

Rules of Ashtadhyayi
The initial sutras which are of adequate importance are:
* Vraddhir Adaich
* Adet Gunah

In such sutras, the capital letters are specially formed meta-linguistic symbols, which are known as `IT` markers or Anubandhas. The N and C signify the Shiva Sutras 3 (e, o, N), and 4 (ai, au, C) respectively. These form the Pratyaharas (comprehensive descriptions), aiC, eN, that symbolize the listing of phonemes e, o and ai, au respectively. The `Ta` (T), which appears in both the sutras, is an IT marker as well. According to the Sutra 1.1.70, it signifies that the previous phoneme does not signify a listing, but rather an individual phenome that involves all the features, including pronunciation and nasality. The two sutras can also be interpreted as Vrddhi, that indicates the phenomes a, ai, au; and Guna, that indicates the phenomes a, e, o. Anubandhas or ITs are expalined in P. 1.3.2 via P. 1.3.8. These explanations point only to the grammar and which is clarified by Upadese, in P. 1.3.2, and persists in the next six rules by Anuvrtti.

Ancillary Texts of Ashtadhyayi
There are three related texts to Ashtadhyayi, of which, the Ganapatha and Dhatupatha are lexicography based lists, and the Shiva sutras are concise and systematic listing of phonemes. The Shiva Sutras explains a phonemic system within the first fourteen lines prior to the Ashtadhyayi. This system depicts various clusters of phonemes which are vital in the Sanskrit morphology. The Dhatupatha is a glossary of verbal roots in Sanskrit. It is prepared by the present 10 classes of Sanskrit. The Ganapatha is a listing of collections of archaic nominal stems that utilised in the Ashtadhyayi.

Towards the conclusion of Ashtadhyayi, there is a lexicon, containing the root words, suffixes and prefixes, known as Dhatu Path. With its profusion of words, grammar of Sanskrit has the ability to generate new words for new concepts.