ABSTRACT
References from publications are at the same time citations to other publications. This entry introduces some of the practical uses of citation data in science and scholarship. At the individual level citations identify and permit the retrieval of specific editions of works, while also suggesting their subject matter, authority, and age. Through citation indexes, retrievals may include not only the earlier items referred to by a given work, but also the later items that cite that given work in turn. Some technical notes on retrieval are included here. Counts of citations received over time, and measures derived from them, reveal the varying impacts of works, authors, journals, organizations, and countries. This has obvious implications for the evaluation of, e.g., library collections, academics, research teams, and science policies. When treated as linkages between pairs of publications, references and citations reveal intellectual ties. Several kinds of links have been defined, such as cocitation, bibliographic coupling, and intercitation. In the aggregate, these links form networks that compactly suggest the intellectual histories of research specialties and disciplines, especially when the networks are visualized through mapping software. Citation analysis is of course not without critics, who have long pointed out imperfections in the data or in analytical techniques. However, the criticisms have generally been met by strong counterarguments from proponents.
