Due to swift growth and development of centralized cooperative bibliographic services and resource sharing, it becomes evident that a standard and foolproof system is required to avoid the mistakes in the process of cataloging. AACR2R and MARC 21 is such standard system, where in AACR2R use in the production of catalogues and the MARC 21 alleviate the exchange of bibliographic and concerned information. MACR 21 support the revised rules of AACR2R for incorporating resources both in print (loose-leaves) and electronic format. This book aims to maintain the tradition established by AACR2 and MARC 21 and attempts to satisfy the same aims that is to furnish a clear and comprehensive overview of modern cataloging theory, policy and practice and to provide a depth description of different fields of AACR2R into MARC21.