The Harivaṃśa has usually been seen as a later addition appended to the Mahābhārata, and so the Mahābhārata has usually been understood without it. This article first introduces an alternative approach, whereby these two texts are viewed as a single whole, and justifies that approach on the basis of the details presented in Mbh 1.2. Then the Harivaṃśa’s narrative mechanics are summarized, to contextualize what follows. The main body of the article offers three kinds of answer to the title question (...) of what difference the Harivaṃśa makes to the Mahābhārata. The first answer is theological: the Harivaṃśa emphasizes the divine level of the Mahābhārata story as the story of the gods descending to help the earth. The second answer is narratological: the Harivaṃśa continues and completes the story of Janamejaya begun in Mbh 1, thus emphasizing his role for the text as a whole. The third answer is structural: if the Mahābhārata includes the Harivaṃśa then the whole text can be studied and analyzed as a macrocompositional unit. The “Mahābhārata as a whole” has been the subject of collaborative study in recent years, and this article continues that study, with regard to a fuller whole. The article, unlike that whole, is short, sketchy, and provisional. It looks forward to further and corrective studies in all the sketched areas, and more. (shrink)