This book constitutes the thoroughly refereed post-proceedings of the 4th International Workshop on Implementing Automata, WIA'99, held in Potsdam, Germany, in July 1999. The 16 revised full papers presented were carefully selected and improved during two rounds of reviewing and revision. The papers are devoted to issues of implementing automata of various types important for areas such as parsing, finite languages, computational linguistics, speech recognition, image and signal processing, and systems analysis.