The "Investigations Explicating the States of Existents" (Taḥqīqāt dar bayān-e ahwāl-e mawjūdāt) is an exciting set of issues in philosophy and philosophical theology examined by Mullā Shamsā Gīlanī (d. 1064/1654), a distinguished student of Mīr Dāmād (d. 1040/1631). Written in the last few years of his life, it represents a phase in the intel-lectual history of Safavid Iran in which, increasingly, works were written in Persian engaging with the philosophical traditions that had previously been penned in Arabic. The text demonstrates a deep knowledge of debates contempo-rary to Mullā Shamsā as well as of the preceding Avicennan (both directly in the line of his students as well as through Avicennan philosophical theology or kalam) and Illuminationist traditions. The book itself takes up twenty issues ranging from the self-evident nature of being and his known critique of the positions of Mullā Ṣadrā (d. 1035/1636) on the primacy of being and its modulation through to the resurrection of bodies and the corporeal nature of the afterlife as well as Mullā Shamsā’s proof for the impossibility of an actual infinity (an old problem of ancient mathematics). The text provides further evidence for why we should engage with the “lesser” known figures of the Safavid period to produce a richer picture of intellectual life. This work is thus an essential proof text for the continuing vitality of intellectual life in post-classical Islamic thought and for the central role of Safavid Iran in the intellectual renaissance of the period before the onset of colonial intervention in the region and the epistemological disruption brought in its wake.