- Gīwargīs I. (660–680): Ostsyrische Christologie in frühislamischer Zeit, Wiesbaden: Harrassowitz, 2016 (Göttinger Orientforschungen, I. Reihe: Syriaca, Band 50).
- The Making of Syriac Jerusalem: Representations of the Holy City in Syriac Literature of Late Antiquity and the Middle Ages, London & New York: Routledge, 2023 (Routledge Studies in the Early Christian World).
- Soul and Body: Diseases, Remedies, and Healing in Middle Eastern Religious Cultures and Traditions, Leiden and Boston: Brill, 2023 (Studies on the Children of Abraham, 10).
- Teaching and Learning the Norms of Life and Faith: Pedagogues, Educators, and Their Heritage in Abrahamic Religions, Tübingen: Mohr Siebeck (SERAPHIM Collection – Studies in Education and Religion in Ancient and Pre-Modern History in the Mediterranean and Its Environs), forthcoming.
Recently, Dr. Popa identified parts of an early Ḥarklean manuscript previously thought to be lost. His findings were published in the article “An Early Ḥarklean Version in a Syriac Gospel Fragmentary Manuscript (MS OR 403)”, Journal of Biblical Literature 143, no. 4 (2024): 717–47.