This book is dedicated to Andrzej Ehrenfeucht on the occasion of his 65th birthday. On personal invitation by the volume editors, 22 internationally well-known scientists from mathematical logics and theoretical computer science participated in this project honoring an excellent scientist with excellent papers centered around his scientific work. The 22 invited papers are presented in topical sections on model theory, games and logic, graphs and algorithms, pattern matching and learning, combinatorics of words, algebra of languages, formal language theory, and computational molecular biology.