The problem of the comprehensiveness of the Quran and its scope is an important Quranic issue and has a pivotal role in its understanding and interpreting. For determining the realm of the Quran, the researchers have stated reasons from the Quranic verses. The most important of them is “الْکِتَابَ تِبْیَانًا لِکُلِ شَیْءٍ وَنَزَلْنَا عَلَیْکَ” (and we have sent down to you the Book as clarification for all things). In spite of being presented the precious debates over this issue, its analysis makes it be clearer on the angles. This note with analytic and descriptive method has studied the exegetists’ opinions about clarifying the Quran. Considering the concept of « تبیان » the exposition (clarification), the way determining the teachings and knowledge in the Quran and the Islamic traditions relating to the comprehensiveness of the Noble Quran is a sign of everything which needs to be clarified (determined). Therefore, the Quran exposes everything including everything relates to the guidance and has religious signs and also everything which is non-religious and not connecting to the religious in appearance. Although, some details have been stated in detail and some others have been presented briefly (summarily) in the Quran and the Quran, itself, hands the explanation of them over to the sunnah -practice- of the prophet (peace be upon him) and Infallibles and the rational principles which are taken sayings and practical from them.