ABHIDAMMA TRADITION

The Pāli Canon,  the scriptures of Theravāda Buddhism, has three general categories called pitaka, from Pali pitaka, meaning "basket."  The canon is traditionally known as the Tipitaka (Sanskrit: Tripitaka) "the three baskets."  They are as follows:

1.Vinaya Pitaka (discipline basket), dealing with rules for monks and nuns.
2.Sutta Pitaka (sutra/sayings basket), discourses, mostly ascribed to the Buddha, but some to disciples.
3.Abhidhamma Pitaka, variously described as philosophy, psychology, metaphysics, etc.

Regarding the Abhidhamma Pitaka (abhidhammapiṭaka), tradition holds that the Buddha thought it out immediately after his enlightenment, then taught it to the gods some years later.  The Buddha then repeated it to one of his chief disciple Sariputta who then handed it on to the disciples.

Scholars, however, generally date the Abhidhamma to some time around the third century BCE, one hundred to two hundred years after the death of the Buddha. The consensus therefore is that the Adhidamma does not, for the most part, represent the words of the Buddha himself so much as the words of his disciples and commentators.

The Abhidhamma Pitaka consists of seven books:

Dhammasangani
Vibhanga
Dhatukatha
Puggalapannatti
Kathavatthu
Yamaka
Patthana

The importance of the Abhidhamma Pitaka is suggested by the fact that it came to have, like much of the canon, not only a commentary and a subcommentary on that commentary, but even a subsubcommentary on that subcommentary.

On the other hand, this relentless sub-commenting might be illustrative of what has been called "shastra-vasna" or "the lust for scriptures." 

In more recent centuries, Burma, now called Myanmar, has become the main center of Abhidhamma studies.