The purpose of this book is manyfold: to shed light on the state of the art on this new frontier; to establish common understanding; to assimilate what we have; and to lay a foundation upon which various aspects of visual programming can be focused and examined. The book is aimed at people who are interested in learning something about visual programming. Potential users may find it useful to know what visual programming is. Researchers and software developers in this wide area may find it useful to relate their own work to other efforts. People whose expertise is not in this field may want to satisfy their curiosity regarding the state of the art. It would be helpful if the reader has a reasonable appreciation of the capabilities of a computer system. But this prerequisite is not particularly demanding, because it is not necessary to understand all the details in order to grasp the thrust of this book. What is important is the basic ideas conveyed. I hope that the book will prove suitable for anyone who wishes to broaden his general knowledge of the field. This book is both a tutorial and a survey. Because it is a tutorial, I have decided not to include commercial products in the marketplace unless the principles underlying the commercial product have been reported in the literature. For my purpose, it is more important to put together the multiplicity of ideas that have shaped the current state of the art, and to discuss the reported efforts that have gone into making visual programming an exciting and promising field.