The Mahīśāsaka (Sanskrit: महीशासक; traditional Chinese: 化地部; ; pinyin: Huàdì Bù; Vietnamese: Hóa địa bộ) is one of the early Buddhist schools according to some records. Its origins may go back to the dispute in the Second Buddhist Council at Vaishali. The Dharmaguptaka sect is thought to have branched out from the Mahīśāsaka sect toward the end of the 2nd or the beginning of the 1st century BCE.

There are two general accounts of the circumstances surrounding the origins of the Mahīśāsakas. The Theravādin Dīpavaṃsa asserts that the Mahīśāsaka sect gave rise to the Sarvāstivāda sect. However, both the Śāriputraparipṛcchā and the Samayabhedoparacanaćakra record that the Sarvāstivādins were the older sect out of which the Mahīśāsakas emerged. Buswell and Lopez also state that the Mahīśāsaka was an offshoot of the Sarvāstivādins, but group the school under the Vibhajyavāda, "a broad designation for non-Sarvastivāda strands of the Sthaviranikaya", which also included the Kāśyapīya.

The Mahīśāsaka originated in Mahishmati in the Avanti region of India, from which they derive their name. The Mahīśāsaka sect founder was a monk named Purāṇa, who is venerated at length in the Mahīśāsaka Vinaya, which is preserved in the Chinese Buddhist canon.

From the writings of Xuanzang, the Mahīśāsaka are known to have been active in Kashmir in the 4th century CE. Xuanzang records that Asaṅga, an important Yogācāra master and the elder brother of Vasubandhu, received ordination into the Mahīśāsaka sect. Asaṅga's frameworks for Abhidharma writings retained many underlying Mahīśāsaka traits. André Bareau writes:

[It is] sufficiently obvious that Asaṅga had been a Mahīśāsaka when he was a young monk, and that he incorporated a large part of the doctrinal opinions proper to this school within his own work after he became a great master of the Mahāyāna, when he made up what can be considered as a new and Mahāyānist Abhidharma-piṭaka.

The Mahīśāsaka are believed to have spread to southern India including Nāgārjunakoṇḍā, and even as far as the island of Sri Lanka. According to A. K. Warder, the Indian Mahīśāsaka sect also established itself in Sri Lanka alongside the Theravāda, into which they were later absorbed.

In the 7th century CE, Yijing grouped the Mahīśāsaka, Dharmaguptaka, and Kāśyapīya together as sub-sects of the Sarvāstivāda, and stated that these three were not prevalent in the "five parts of India", but were located in the some parts of Oḍḍiyāna, the Kingdom of Khotan, and Kucha.

Between 148 and 170 CE, the Parthian monk An Shigao came to China and translated a work which describes the color of monastic robes (Skt. kāṣāya) utilised in five major Indian Buddhist sects, called Da Biqiu Sanqian Weiyi (Chinese: 大比丘三千威儀). Another text translated at a later date, the Śāriputraparipṛcchā, contains a very similar passage corroborating this information. In both sources, members of the Mahīśāsaka sect are described as wearing blue robes. The relevant portion of the Mahāsāṃghika Śāriputraparipṛcchā reads, "The Mahīśāsaka school practice dhyāna, and penetrate deeply. They wear blue robes."