Libraries organize information resources on shelves, keeping related items together and unrelated items apart. This is to facilitate the easy location of, and thus access to, information resources. Systematic methods, widely adopted for the organization of library materials and its recording for the use of readers, came into being little more than a century ago. In 1876 Melvil Dewey developed a systematic scheme of library classification that eventually became one of the most widely used tools for organizing library materials on library shelves. Since then a number of library classification schemes have been developed to aid the process of organizing library materials in a systematic manner. This chapter begins with a discussion of the basic principles of library classification, and outlines the major types of library classification schemes and their attributes. It then discusses the characteristic features of some well known classification schemes such as Dewey Decimal Classification (DDC), Universal Decimal Classification (UDC), Library of Congress Classification (LC), Bibliographic Classification (BC) and Colon Classification (CC). The discussion places more emphasis on DDC because of its popularity and wide usage in the library world. Use of library classification in the organization of electronic resources is also considered, and the chapter ends with a brief discussion of a new type of classification called social classification, or folksonomy.