The first centuries after Śākyamuni Buddha’s death saw the rise of multiple schools of thought and teacher lineages within the Buddhist community as it spread throughout the Indian subcontinent. These new forms of scholarly monastic communities had distinct theoretical and practical interests and, in their efforts to organize, interpret, and reexamine the Buddha’s scattered teachings, they developed a particular system of thought and method of exposition called Abhidhamma (Sanskrit, Abhidharma). The term abhidhamma refers both to the doctrinal investigations of this new movement and to the body of texts yielded by its systematic exposition of Buddhist thought. This body of literature includes the third of the “three baskets” of the Buddhist canon, namely, the Abhidhamma-piṭaka, its commentaries, and later exegetical texts. Both as an independent literary genre and a branch of thought and inquiry, Abhidhamma is to be contrasted with the Suttanta thought-world, the framework of the Buddha’s discourses. The hallmark of the Abhidhamma mindset is its systematic account of sentient experience in the form of an overarching inquiry known as the “dhamma theory”. This chapter provides a concise exposition of the transition from the Suttanta thought-world to the canonical and post-canonical Abhidhamma, with particular attention to the role of the dhamma theory in this transition.