Probably the first widely used controlled vocabulary for searching information was the Subject Heading Authority List issued by the National Library of Medicine.
"The first official list of subject headings published by the National Library of Medicine appeared in 1954 under the title Subject Heading Authority List. It was based on the internal authority list that had been used for publication of Current List of Medical Literature which in turn had incorporated headings from the Library's Index-Catalogue and from the 1940 Quarterly Cumulative Index Medicus Subject Headings. With the inception of Index Medicus in 1960, a new and thoroughly revised Medical Subject Headings [MeSH] appeared.
"With the 1954 Subject Heading Authority List, there appeared a 'Categorical Listing' of standard subheadings. 'Abnormalities,' for instance, was listed as a standard subheading for use with terms for organs, tissues, and regions, and 'anesthesia and analgesia' was to be used under surgical procedure headings. But such subheadings could be used only for subject headings which fell within the category of headings to which they were to be applied. There were over 100 such subheadings, some of which varied only slightly according to the category of main heading with which they were used. For instance, 'therapeutic use' was used under physical agents and drugs and chemicals, and 'therapy' was used with diseases. In the 1960 Medical Subject Headings, the number of subheadings was reduced to sixty-seven. They could be used under any kind of main heading if the combination was not patently foolish or impossible. These sixty-seven subheadings were applied with more generalized meanings. For instance, the subheading "therapy" was used to mean 'therapy of,' 'therapeutic use of' or just 'therapeutic aspects.' Though this solution was simpler, many problems still remained. The use of one subheading might prevent the use of another. For instance, if a paper covered the etiology, pathology, and therapy of a disease, it might occur without further subdivision, or it might occur under the subheading which seemed most appropriate to the indexer. If 'therapy' was chosen, the article would be lost to the searcher looking for the etiology of the disease under the subheading 'etiology.' In addition, if the subheading 'diseases' had been appended to the term for an anatomic part, it would not be possible to subdivide further for the therapy or complications of such diseases. A related problem was the overlap in meaning of the subheadings themselves. It was difficult, for example, to decide whether a paper on chemical biosynthesis fit best under 'chemistry' or 'metabolism.'
"Categorized lists of terms were printed for the first time in the 1963 Medical Subject Headings and contained thirteen main categories and a total of fifty-eight separate groups in subcategories and main categories. These categorized lists made it possible for the user to find many more related terms than were in the former cross-reference structure. In 1963, the second edition of Medical Subject Headings contained 5,700 descriptors, compared with 4,400 in the 1960 edition. Of the headings used in the 1960 list, 113 were withdrawn in favor of newer terms. In contrast, the 2009 edition of MeSH contains 25,186 descriptors.
"In 1960, medical librarianship was on the cusp of a revolution. The first issue of the new Index Medicus series was published. On the horizon was a computerization project undertaken by the National Library of Medicine (NLM) to store and retrieve information. The Medical Literature Analysis and Retrieval System (MEDLARS) would speed the publication process for bibliographies such as Index Medicus, facilitate the expansion of coverage of the literature, and permit searches for individuals upon demand. The new list of subject headings introduced in 1960 was the underpinning of the analysis and retrieval operation. MeSH was a new and thoroughly revised version of lists of subject headings compiled by NLM for its bibliographies and cataloging. Frank B. Rogers, then NLM director, announced several innovations as he introduced MeSH in 1960" (http://www.nlm.nih.gov/mesh/2009/introduction/intro_preface.html#pref_hist. accessed 05-04-2009).