This collection of papers arose from a series of lectures for workers in computer science and other disciplines. The lectures were intended to familiarize them with some of the most exciting advanced computer based systems for the conceptualization, design, implementation, simulation, and logical analysis of applications in these disciplines. The collection presents some strong motivational points for the use of theory based systems in the areas of functional programming, concurrency, simulation, and automated reasoning, highlighting some of their advantages and disadvantages relative to conventional systems. The papers are mostly the work of individuals who were among the originators of the systemspresented. The volume is intended as a contribution to narrowing the learning gap facing conventional computer users when they wish to use advanced theory based systems. The papers are meant for a wide audience and should not require great mathematical sophistication for their comprehension. The papers contain numerous references for those wishing to pursue a topic in greater depth.