Which parva does the book Mahabharata begin?

The Mahabharata starts with the Adi Parva.

This is the first of 18 books of Mahabharata ." Adi" (आदि, Ādi) is a word that signifies "first". It incorporates a diagram of substance from the eighteen books, alongside the book's centrality. The historical backdrop of the Bharatas and the Bhrigus are portrayed.