This book is the first in-depth study of the Saiva oeuvre of the celebrated polymath Appaya Diksita (1520-1593). Jonathan Duquette documents the rise to prominence and scholarly reception of Sivadvaita Vedanta, a Sanskrit-language school of philosophical theology which Appaya single-handedly established, thus securing his reputation as a legendary advocate of Saiva 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 Sivadvaita exegesis, Srikantha's Brahmamimamsabhasya; identifies Appaya's key intellectual influences and opponents in his reconstruction of Srikantha'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 Sivadvaita Vedanta, the Sivarkamanidipika, this book demonstrates that Appaya's Saiva oeuvre was mainly directed against Visistadvaita Vedanta, the dominant Vaisnava 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.