This collection of papers arose from a series of lecturesfor workers in computer science and other disciplines. Thelectures were intended to familiarize them with some of themost exciting advanced computer based systems for theconceptualization, design, implementation, simulation, andlogical analysis of applications in these disciplines. The collection presents some strong motivational points forthe use of theory based systems in the areas of functionalprogramming, concurrency, simulation, and automatedreasoning, highlighting some of their advantages anddisadvantages relative to conventional systems. The papersare mostly the work of individuals who were among theoriginators of the systemspresented. The volume is intended as a contribution to narrowing thelearning gap facing conventional computer users when theywish to use advanced theory based systems. The papers aremeant for a wide audience and should not require greatmathematical sophistication for their comprehension. Thepapers contain numerous references for those wishing topursue a topic in greater depth.