The Quran is the Holy book of Islam. It is the record of the exact words revealed by God through the Angel Gabriel to the Prophet Muhammad. It was memorized by Muhammad and then dictated to his companions. The text of the Quran was cross-checked during the life of the Prophet. The 114 chapters of the Quran have remained unchanged through the centuries.
Taken from: http://www-scf.usc.edu/~uscmhsa/aboutislam.html