Information retrieval (IR) is about making systems for finding documents or information. Knowledge Organization (KO) is the field concerned with indexing, classification, and repre-senting documents for IR, browsing, and related processes, whether performed by humans or computers. The field of IR is today dominated by search engines like Google. An important dif-ference between KO and IR as research fields is that KO attempts to reflect knowledge as depicted by contemporary scholarship, in contrast to IR, which is based on, for example “match” techniques, popularity measures or personalization principles. The classification of documents in KO mostly aims at reflecting the classification of knowledge in the sciences. Books about birds, for example, mostly reflects (or aims at reflecting) how birds are classified in ornithology. KO therefore re-quires access to the adequate subject knowledge, which, however, is often characterized by disa-greements. At the deepest layer, such disagreements are based on philosophical issues best characterized as “paradigms”. No IR technology and no system of knowledge organization can ever be neutral in relation to paradigmatic conflicts, and therefore such philosophical problems represent the basis for the study of IR and KO.