The Buddhist canon is composed of the "three baskets" (tri-pitaka), i.e. the Sutra-pitaka, the Vinaya-pitaka, and the Abhidharma-pitaka. The various Buddhist traditions recognize that the sutras and the Vinaya were delivered by the Buddha but the Abhidharma texts were composed by later Buddhists to elucidate and systematize the essential doctrines in the sutras. The prototype of abhidharma had already appeared in a number of sutras. After schisms occurred in Buddhism, some sects or schools developed their own Abhidharma-pitaka. In this essay, I explore how abhidharma was developed from the style of sutras into the Abhidharma-pitaka and how the extant Abhidharma-pitakas of three schools interpreted, classified, and systematized the Buddha's discourses in different ways, thereby creating their own methods of Abhidhannic discussion. The sutraz were tailored to the needs of a wide variety of audiences and were expounded under diverse circumstances to individuals with different capacities for comprehension. By contrast the typical Abhidharmic way of discussion, while disregarding the narratives contained in the sutras, analyzed the Buddha's teaching (Dharma) into all possible "ultimately real" elements and classified them according to various schemes of taxonomy in order to construct a complete doctrinal system. This essay will attempt to answer the following questions: Who were the people that the Abhidhanna-pitaka was meant to serve? What motivated some sects to compose the Abhidharma-pitaka? Which factors brought about the rise of the Abhidharma-pitakat?