This book constitutes the refereed proceedings of the 26th Conference on Current Trends in Theory and Practice of Informatics, SOFSEM'99, held in Milovy, Czech Republic, in November/December 1999. The volume presents 19 invited survey articles by leading researchers together with 18 revised full research papers selected from 45 submissions. The areas covered include trends in theory, core technologies, software and information engineering, from data to knowledge, and advanced applications.