The Mahābhāṣya (Sanskrit: महाभाष्य, IPA: [məɦɑːbʱɑːʂjə], great commentary), attributed to Patañjali, is a commentary on selected rules of Sanskrit grammar from Pāṇini's treatise, the Ashtadhyayi, as well as Kātyāyana's Varttika, an elaboration of Pāṇini's grammar. It is dated to the 4th century BCE.
Patañjali is one of the three most famous Sanskrit grammarians of ancient India, other two being Pāṇini and Kātyayana who preceded Patañjali (dated to c. 150 BCE). Kātyayana's work (nearly 1500 vārtikas on Pāṇini) is available only through references in Patañjali's work.
It was with Patañjali that the Indian tradition of language scholarship reached its definite form. The system thus established is extremely detailed as to shiksha (phonology, including accent) and vyakarana (grammar and morphology). Syntax is scarcely touched, because syntax is not important in this highly inflexional language, but nirukta (etymology) is discussed, and these etymologies naturally lead to semantic explanations. People interpret his work to be a defense of Pāṇini, whose Sutras are elaborated meaningfully. Patañjali also examines Kātyāyana rather severely. But the main contributions of Patañjali lies in the treatment of the principles of grammar enunciated by him.