This article presents a fresh assessment of evidence for the existence of Śaṅkara’s ‘longer’ commentary on the Aitareyopaniṣad, a sub-section of the Aitareyāraṇyaka (AiĀ). While most printed editions of the Bhāṣya consider that it covers only three adhyāyas of the Āraṇyaka (AiĀ 2.4-6/7), a much more comprehensive work, bearing on the whole of AiĀ 2 and 3, is preserved in manuscripts. In the first part of the article, I argue that the ascription of this ‘longer’ gloss to Śaṅkara is likely to be justified, building on previous scholarship (A.B. Keith, S.K. Belvalkar) as well as on my own inspection of two manuscripts of the work, newly identified in the Cambridge University Library. Questions are also raised as to the constitution of the Upaniṣadic canon(s) and the role of commentaries in that process. The second part of the essay provides a comprehensive survey of the material (manuscript and print) available for a first critical edition of this important, though mostly neglected work by the great Vedāntin.