This book is the first in-depth study of the Śaiva oeuvre of the celebrated polymath Appaya Dīkṣita (1520-1593). Jonathan Duquette documents the rise to prominence and scholarly reception of Śivādvaita Vedānta, a Sanskrit-language school of philosophical theology which Appaya single-handedly established, thus securing his reputation as a legendary advocate of Śaiva 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 Śivādvaita exegesis, Śrīkaṇṭha's Brahmamīmāmsābhāṣya; identifies Appaya's key intellectual influences and opponents in his reconstruction of Śrīkaṇṭha'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 Śivādvaita Vedānta, the Śivārkamanidīpikā, this book demonstrates that Appaya's Śaiva oeuvre was mainly directed against Viśiṣtādvaita Vedānta, the dominant Vaiṣṇava 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.