The central term in Tamil Śaiva religious vocabulary is aruḷ, designating Śiva's fundamental principle. It is widely regarded that Śiva's aruḷ spawned the cosmos, and to a practicing Śaiva, only Śiva's aruḷ can free a soul from the cycle of samsāra or rebirth. In a Śaiva theological context, the term debuts in medieval bhakti (devotional) hymns of the nāyan̲mār (poet-saints); over the course of four centuries (ca. 6th - 9th cents CE) the theological nuances of the term became increasingly intricate. In the last major devotional work produced, the Tiruvācakam (ca. 9th cent CE), Māṇikkavācakar expanded the semantic latitude of aruḷ, using it in ways that the previous Śaiva poets had not. Māṇikkavācakar created a space for arul to become the Śaiva identity mark par excellence. He used the term to indicate an array of theological aspects--Śiva himself, Śiva's grace, any action that Śiva undertakes, the path of knowledge that assists devotees in understanding the nature of the soul, and the mercy and compassion that Śiva has for his servants. While this list is not exhaustive, it points to the semantic breadth of arul as a Śaiva theological concept. This dissertation is an analysis of the semantic evolution of the concept arul through three genres of Tamil literature: classical (caṅkam) heroic and love poetry, and medieval Śaiva devotional poetry. I utilize a variety of texts for the project. From the eight anthologies of cankam poetry, I translate and analyze poems from the Pur̲anān̲ūru, Aiṅkur̲un̲ūru, Kur̲untokai, Akanān̲ūr̲u (ca. 1st century BCE to 4th century CE). From Śaiva bhakti literature, I focus on Māṇikkavācakar's Tiruvācakam. In reading from these texts, I trace the semantic continuity and interruption between the classical secular poetry and the medieval devotional poetry. I argue, among other things, that the cultural underpinnings of the concept remain intact as the term becomes incorporated in the technical vocabulary of Tamil Śaivism. The Śaiva authors were thus able to develop a new and unique style of religious literature that resonated with the cultural and literary past. / text