This book constitutes the carefully refereed proceedings of the 4th International Workshop on Applied Parallel Computing, PARA'98, held in Umea, Sweden, in June 1998. The 75 revised papers presented were carefully reviewed and selected for inclusion in the book. The papers address a variety of topics in large scale scientific and industrial-strength computing, in particular high-performance computing and networking; tools, languages, and environments for parallel processing; scientific visualization and virtual reality; and future directions in high-performance computing and communication.