The Multilingual Universal Decimal Classification Summary - UDC Summary (udcS) for short - represents a selection of around 2,600 classes extracted from the UDC Master Reference File (UDC MRF) 2011 which contains over 70,000 classes. The selection comprises main numbers, common auxiliary numbers and special auxiliary numbers and it represents even coverage of all areas of knowledge as contained by the scheme. UDC is updated annually and UDC Summary represents always the latest version of UDC.