The Universal Decimal Classification (UDC) was devised in the early 20th century by two Belgians, Paul Otlet and Henri La Fontaine. Otlet and La Fontaine had conceived the idea of making a bibliography of all works published since the invention of printing – a project that was just about feasible a hundred years ago – and they wanted a system for the subject organization of their bibliography.

At that time there were several bibliographic classification schemes available to them, but the one that impressed them the most was Dewey's Decimal Classification, then in its fifth edition. They did not find in the DDC exactly what they wanted, and so they made some amendments and additions of their own to create what was the first edition of the Universal Decimal Classification, published between 1905 and 1907.

UDC is thus unique among the well-known schemes in that it wasn't originally intended to arrange a physical collection of documents, but rather to organize a bibliography in the form of a card catalogue. As a consequence, the decisions that were made about its structure and function at that time placed the main emphasis on its use as a tool for retrieval. Great importance was attached to its ability to provide very detailed subject description, particularly for complex topics, and this was achieved at the expense of simplicity in the notation. This has continued to be an important characteristic of UDC, which means it is favoured in situations where retrieval is more important than browsing.

General characteristics of UDC

The scheme is very much more flexible than the enumerative schemes we've considered in previous chapters, and it can be used to create very detailed classmarks for documents with complicated subject content. As a result it has been a popular choice for use in scientific and technical libraries, and those that deal with large amounts of technical literature and reports. In the UK it can be found in a number of research establishments such as the Polar Research Institute, in government libraries at the Ministry of Defence and DEFRA, and in large academic scientific collections, such as the library at Imperial College (although Imperial is currently in the process of re-classifying).