This special issue consists of some of the best lectures given at the Workshop on Formal Languages and Automata (WFLA) in Iasi, Romania, September 2 - 3, 1999. This workshop was a satellite event of the conference Fundamentals of Computation Theory (FCT'99) held also in Iasi, Romania, August 30 - September 2, 1999. The workshop was organized by the University A.I. Cuza, Iasi, Romania.

I want to take this opportunity to mention the crucial role of the members of the Program Committee of this workshop: Profs. Erzsebet Csuhaj-Varju, Alica Kelemenova, Toader Jucan, Carlos Martin-Vide and Yurii Rogozhin. Without their invaluable contribution, the workshop could not have taken place.

Also, I would like to thank all contributors to this volume for their enthusiastic response to the initial call for papers, which has finally resulted in important contributions that can be found next. In the meantime, I express my sincere gratitude to all anonymous referees for their careful reviewing of the papers submitted.

Finally, I am grateful to Professor Dr.Dr.h.c. Hermann Maurer and to Springer for their invitation to edit this volume as a special issue of the Journal of Universal Computer Science (J.UCS).