This book constitutes the refereed proceedings of the 23rd British National Conference on Databases, BNCOD 23, held in Belfast, Northern Ireland, July 2006. The volume presents 12 revised full papers and 6 revised short papers, together with 2 invited lectures and 13 poster papers. Topical sections include data modelling and architectures and transaction management, data integration and interoperability and information retrieval, query processing and optimisation, data mining, data warehousing and more.