This remarkable twelfth-century Qur’anic commentary by Muḥammad b. ʿAbd al-Karīm al-Shahrastānī is preserved in a single manuscript in Tehran and marks the achievement of a lifelong, arduous quest for knowledge. The introduction and opening chapter of this virtually unknown work are presented here in a bilingual edition with an introduction and contextual notes by Dr Toby Mayer. In Keys to the Arcana, Shahrastānī breaks down the text of the Qur’an and analyses it from a linguistic point of view, with reference to the history of Qur’anic interpretation. The author’s aim is to use an elaborate set of complementary concepts – the ‘keys’ of the work’s title – to unearth the esoteric meanings of the Qur’anic verses. Dr Mayer’s meticulous translation of Shahrastānī’s Introduction and Commentary on Sūrat al-Fātiḥa, supplemented by the Arabic text, allows access to this unique work for the first time.