The field of information retrieval, the methods of indexing and storing the vast number of scientific documents which have been produced in recent years is surveyed. Information retrieval utilizes coordinate indexing - that is, listing documents under all the topics they contain and searching for them by two or more terms. There are two principal types of indexing: one using a predetermined list of terms into which all documents must be fitted and the other allowing free choice of the terms found in the documents themselves. Elaboration of these methods and the difficulty of developing a list of indexing terms are also discussed. An information retrieval system may consist of an index only, an index with an abstract, or an entire document with an index. The mechanical equipment used may range from punched cards through IBM cards to complex computers and micro photographic systems. The experiences of various organizations with different combinations of equipment and methods are discussed.