This book constitutes the refereed proceedings of the First International Conference on Data Warehousing and Knowledge Discovery, DaWaK'99, held in Florence, Italy in August/September 1999. The 31 revised full papers and nine short papers presented were carefully reviewed and selected from 88 submissions. The book is divided in topical sections on data warehouse design, online analytical processing, view synthesis, selection, and optimization, multidimensional databases, knowledge discovery, association rules, inexing and object similarities, generalized association rules and data and web mining, time series data bases, data mining applications and data analysis.