Visual languages are ubiquitous in human cultures and range from informal ambiguous sketches to rigorously defined technical diagrams such as electronic circuit designs or musical notation. They have become a key component of human-computer interaction with the advent of GUIs and sophisticated input devices. This book provides a broad-ranging survey of our current understanding of visual languages and their theoretical foundations. Its main focus is the definition, specification, and structural analysis of visual languages by grammars, logic, and algebraic methods and the use of these techniques in visual language implementation. Consequently, the researcher in formal language theory, HCI, artificial intelligence, and computational linguistics will find this an invaluable guide to the current state of research in this field.