This discussion of the nature of classification schemes and their functions focuses on the differing classification systems of North American and European-type libraries. The functions are bibliothecal, bibliographical, and cognitive. The bibliothecal function concerns the physical location of items within a library (e.g., the Dewey Decimal and the Library of Congress systems). Its efficiency and effectiveness depend most on: (1) diversity of forms, age of materials, user levels, and size of the collection; and (2) the flexibility, size, and layout of the physical library quarters. The bibliographical function attempts to organize the knowledge and information contained within any given document. Its success depends not on the physical quarters or diversity of library materials, but on the user's educational sophistication, academic or informational needs, and cultural, philosophical, and political background. The cognitive function addresses the assessment of relationships, interrelationships, connections, interconnections, associations, approximation, and relevance to describe the complete identity of items and facilitate retrieval of information. This function involves the formulation of subject descriptors, organizing the descriptors, and assisting the interrogation (searching) of files. It is concluded that one classification system cannot incorporate all three functions, yet libraries should combine at least two of the functions to improve the organization and retrieval of information. (Author/SD)