This volume contains the papers presented at RelMiCS 2001, the 6th Int- national Conference on Relational Methods in Computer Science, and the First Workshop of COST Action 274TARSKI, Theory and Application of Relat- nal Structures as Knowledge Instruments. The conference was held in conference centre Boschoord, Oisterwijk near Tilburg, The Netherlands, from October 16 till October 21, 2001. The conference attracted interest from many parts of the world with contributions from many countries. This conference was a continuation of international conferences/workshops on Relational Methods in...