Data Warehousing and Knowledge Discovery technology is emerging as a key technology for enterprises that wish to improve their data analysis, decision support activities, and the automatic extraction of knowledge from data. The objective of the Third International Conference on Data Warehousing and Knowledge Discovery (Da Wa K 2001) was to bring together researchers and practitioners to discuss research issues and experience in developing and deploying data warehousing and knowledge discovery systems, applications, and solutions. The conference focused on the logical and physical design of data warehousing and knowledge discovery systems. The scope of the papers covered the most recent and relevant topics in the areas of association rules, mining temporal patterns, data mining techniques, collaborative filtering, Web mining, visualization, matchmaking, evelopment and maintenance of data warehouses, OLAP, and distributed data warehouses. These proceedings contain the technical papers selected for presentation at the conference. We received more than 90 papers from over 20 countries, and the program committee finally selected 34 papers. The conference program included one invited talk: "Knowledge Management in Heterogeneous Data Warehouse Environments" by Professor Larry Kerschberg, George Mason University, USA.