This dissertation focuses on the emergence of Buddhist commentaries in Pali and Gandhari as new exegetical genres in first-millennium South Asia, aiming at revealing the diversity of Buddhist commentaries and the multiple ways of interpreting Buddhist canonical texts. Comparing radically different commentaries and situating them in the history of religions, I argue that the Buddhist commentators maintained a tension between doctrinal consistency and methodological diversity in the multireligious world of the mid-first millennium. Specifically, I examine the commentarial styles in the Niddesa and compare them with the various methods of definition adopted in other commentaries, through a case study of the concept “suffering.” I find that, with the transition from oral to written commentaries, the scholastic tradition of Abhidharma/Abhidhamma contributed to the stylistic transition in commentaries and enabled the Buddhist commentators to maintain doctrinal consistency in their scholastic development. This is demonstrated through consideration of the Buddhist hermeneutical handbooks Nettipakaraṇa and Peṭakopadesa, and the Gandhari commentaries in the British Library Kharoṣṭhī fragments, which seek to limit the interpretative possibilities by formulating stringent structural analysis of the root texts. Additionally, the Guidelines (Pali naya) in the Nettipakaraṇa and Peṭakopadesa also shape the teaching event by targeting specific types of audiences. While tracing their literary root to nidāna (source, provenance) in the canonical texts, the narrative commentaries such as the Dhammapada-aṭṭhakathā and Jātaka-aṭṭhakathā, with their temporal structure and narrative art, function as effective didactic tools that convey karmic laws and soteriological goals to the audience. Buddhist semantic derivation and Pali language ideology suggest close interactions with the Vedic semantic derivation (Sanskrit. nirvacana/nirukta) and Pāṇinian grammatical and Mīmāṃsā tradition while offering serious challenges to their Brahmanical rivals. It is likely that the political and religious tensions in mid-first millennium Lanka motivated the Mahāvihārins to express a unique language ideology in their commentaries and to patronise more Pali literary production. The study of the individual texts and traditions refreshes our understanding of the socio- religious contexts that gave birth to variegated Indic Buddhist commentarial literature and demonstrates Buddhist commentaries as a fertile ground for strengthening doctrinal consistency and improving didactic efficacy in interreligious contexts.