This thesis introduces, contextualizes, and closely examines the Gāruḍa Tantras, an early medieval branch of Śaiva scripture that has hitherto not been a proper object of study. The Gāruḍa Tantras were religiously-oriented and divinely-revealed medical manuals whose chief concern was treating snakebite envenomation. Although previously deemed lost, this dissertation establishes the survival and influence of this class of scriptures by drawing on unpublished manuscript sources. The first chapter outlines the scant past research on snakebite and mantras in early South Asian medical systems, and proposes a more nuanced approach based on empathetic skepticism. The long second chapter surveys the theme of snakebite medicine in Sanskrit and Prakrit texts from the Veda down to modern compositions, and establishes the widespread influence of the Gāruḍa Tantras. The third and fourth chapters closely examine the masculine mantra and feminine vidyā systems respectively, with the aim of understanding the intricate levels of meaning encoded in ritual practices. The fifth chapter analyzes Garuḍa as a nonsectarian deity, with particular reference to how his identity functions in the possession ritual at the core of the Gāruḍika's practice. The sixth chapter concludes and recommends directions for future research. Part II of the thesis is an introduction, critical edition, and English translation of nine chapters of the Kriyākālaguṇottara, an early scriptural compilation that preserves a great deal of archaic material from the Gāruḍa Tantras.