<strong>ملخص الدراسة:</strong>

The study concentrates on the extend of applying the ٢١st and ٢٢ndnew editions of Dewy decimal classification system to University ofMosul Central library catalog records to define the authenticated toolsused in assigning classification numbers for the materials cataloged atthe central library and their consequences represented in detectingmistakes and problems which hinder that application through selectinga random intentional sample These samples are mounted to (١٠٠)records chosen from the Arabic shelf list record . The researcherdepends on the analytical descriptive method and the study concludeswith a group of results the most important ones of which are:١- The usage of different tools in classification may cause many casesof confusion and inconsistency.٢- The malcommitment to the modification and reviews whether thecomprehensive or the partial one which the ٢١st and ٢٢nd editionsunderwent.٣- The mistakes in combining, building or selecting a classificationnumber for the cataloged material where the study revealed that ٣٩٪of the sample records were cataloged under wrong classificationnumbers which do not comply with the subject of the catalogedmaterial.The most important recommendations the study presented is: ١- Reliance on a clear and definite policy to be complied by thecatalogers pertaining to using the new editions of the system at thecentral library to cope with the amendments and modifications of thesystem .