The Muslims in general believe that the Quran has been preserved intact and pure by Allah Himself. But what is often forgotten by many is that this preservation necessarily includes the Sunnah of the Prophet Muhammad (S), the practical example of the implementation of the Quran. Hadith is Sunnah in record. How the immense wealth of Hadith literature has been left to us by the Muhaddiths (scholars of Hadith) is an extremely wide, complex study. We publish this short treatise on "the science of Hadith" by the learned Suhaib Hasan with English readers in mind. It is part of our scheme to introduce various aspects of Islam to English readers. May Allah accept it as a good work.