The present study sheds light on very important and common matter in the central libraries in Baghdad. This subject is the selection of classification number. The paper aims at introducing the problems that face the researcher in his searching. Similarly, it shows the role of classification in order to get an easy and quick access to the book(s) required. In spite of the technical devices being used in these libraries, the quick access to the book(s) still seems to be not applicable, unless full and correct data are given about the accessed book(s). The study review samples amounted to 381 books that were classified differently by different libraries. The study recommends to form a unified committee for classification in the central libraries in order to overcome this problem.