The Mahabharata is one of the two most important epics of ancient India. The title may be translated as the great tale of the Bharata dynasty. Authored by sage Veda Vyasa, The Mahabharata, comprising more than 90,000 couplets, usually of 32 syllables, is the longest single poem in world literature. The epic is an important part of the Hindu history and is supposed to be all inclusive. In other words; what is found in Mahabharata may be found elsewhere, but what is not found there will not be found elsewhere. Bhagavad Gita, which is the single most sacred text of Hindu culture is itself a part of Mahabharata.
You can read the original sanskrit version in Devanagiri and Western scripts along with its english translation at internet sacred texts archive (link given below). The Ganguli English translation is cross-linked on a book-by-book basis with the Sanskrit text.