The Puranas hold the accounts of creation and dissolution, of lineages divine and royal, and of the deeds by which the deities are known. Eighteen are counted as Mahapuranas, and the tradition describes their scope through the pancha-lakshana, the five marks a Purana is expected to carry. Many also preserve the sthala mahatmya of particular temples — the account of how a place came to be sacred.
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There are eighteen Mahapuranas, which are all written by Sage Veda Vyasa and eighteen Upapuranas, that together forms the core corpus of Puranic literature.
Source: Puranic canon lists (Vishnu, Bhagavata, Matsya Purana)