This review volume brings together the works of several prominent researchers who had collaborated with Janusz Brzozowski in area of regular expressions and on syntactic semigroups of formal languages, as well as Brzozowski conjecture, dot-depth hierarchy, Communicating Sequential Processes (CSP) and DFA minimization.Contributors of this review volume include Zoltán Ésik, Helmut Jorgensen, Markus Holzer, Martin Kutrib, Ernst Leiss, Jean-Éric Pin, Grzegorz Rozenberg, Arto Salomaa, Kai Salomaa, Andrew Szilard and Bruce Watson.