This volume contains papers selected for presentation at the 31st Annual C- ference on Current Trends in Theory and Practice of Informatics - SOFSEM 2005, held on January 22-28, 2005 in LiptovskyJ an, Slovakia. The series of SOFSEM conferences, organized alternately in the Czech - public and Slovakia since 1974, has a well-established tradition. The SOFSEM conferences were originally intended to break the Iron Curtain in scienti?c - change. After the velvet revolution SOFSEM changed to a regular broad-scope international conference. Nowadays, SOFSEM is focused each year on selected aspects of...