The International UDC Seminar entitled "Classification & Authority Control: Expanding Resource Discovery" took place in the National Library of Portugal in Lisbon, on 29-30 October 2015. This was the fifth in a series of International UDC Seminars.

The programme comprised twenty presentations and six posters. Keynote speaker Prof. Michael K. Buckland opened the conference with observations on the importance of relationships between concepts, semantic linking and their cultural and contextual determination. His talk brought into focus the challenges for knowledge classification and controlled vocabularies in general. A number of presentations that followed gave an insight into authority standards and subject authorities, the structural and modelling issues of classifications and concept relationships as well as name authorities. Several examples of authority control systems supporting classification were presented and several approaches towards classification-based resource discovery without the use of authority control were also suggested.

The conference was attended by 95 delegates from 26 countries comprising information professionals, classification and indexing specialists, researchers, practitioners, students in information and knowledge organization domain.

The proceedings of the conference were published by Ergon.