This book is the first in-depth study of the aiva oeuvre of the celebrated polymath Appaya Dkita (1520-1593). Jonathan Duquette documents the rise to prominence and scholarly reception of ivdvaita Vednta, a Sanskrit-language school of philosophical theology which Appaya single-handedly established, thus securing his reputation as a legendary advocate of aiva religion in early modern India. Based to a large extent on hitherto unstudied primary sources in Sanskrit, Duquette offers new insights on Appaya's early polemical works and main source of ivdvaita exegesis, rkaha's Brahmammmsbhya; identifies Appaya's key intellectual influences and opponents in his reconstruction of rkaha's theology; and highlights some of the key arguments and strategies he used to make his ambitious project a success. Centred on his magnum opus of ivdvaita Vednta, the ivrkamanidpik, this book demonstrates that Appaya's aiva oeuvre was mainly directed against Viitdvaita Vednta, the dominant Vaiava school of philosophical theology in his time and place. A far-reaching study of the challenges of Indian theism, this book opens up new possibilities for our understanding of religious debates and polemics in early modern India as seen through the lenses of one of its most important intellectuals.