The Mūlasarvāstivāda was an early school of Buddhism, developed in India during the 2nd century AD and in decline by the 7th century. Its vinaya lineage has been preserved by Tibetans and Mongolians up to the present, although until recently, only Mulasarvastivadin monks existed - the lineage of the nuns had been lost.

The relationship of the Mūlasarvāstivāda to the Sarvāstivāda school is a matter of dispute; modern scholars lean towards classifying them as independent.I Ching claimed that they derived their name from being an offshoot of Sarvāstivāda, but Buton Rinchen Drub stated that the name was a homage to Sarvāstivāda as the "root" (mūla) of all Buddhist schools. A number of theories have been posited by academics as to how the two are related, which Bhikkhu Sujato summaries as follows: