This book constitutes the refereed proceedings of the 13th East European Conference on Advances in Databases and Information Systems, ADBIS 2009, held in Riga, Latvia, on September 7-10, 2009. The 25 revised papers were carefully reviewed and selected from 93 submissions. Topically, the papers span a wide spectrum of the database and information system. Topics are ranging from query processing and optimization via query languages, design methods, data integration, indexing and caching to business processes, data mining, and application oriented topics like XML and data on the Web.