This book has emerged from my lecture notes for an introductory course in compiler design at ETH Zürich. Several times I have been asked to justify this course, since compiler design is considered a somewhat esoteric subject, practised only in a few highly specialized software houses. Because nowadays everything which does not yield immediate profits has to be justified, I shall try to explain why I consider this subject as important and relevant to computer science students in general.

It is the essence of any academic education that not only knowledge, and, in the case of an engineering education, know-how is transmitted, but also understanding and insight. In particular, knowledge about system surfaces alone is insufficient in computer science; what is needed is an understanding of contents. Every academically educated computer scientist must know how a computer functions, and must understand the ways and methods in which programs are represented and interpreted. Compilers convert program texts into internal code. Hence they constitute the bridge between software and hardware.

Now, one may interject that knowledge about the method of translation is unnecessary for an understanding of the relationship between source program and object code, and even much less relevant is knowing how to actually construct a compiler. However, from my experience as a teacher, genuine understanding of a subject is best acquired from an in-depth involvement with both concepts and details. In this case, this involvement is nothing less than the construction of an actual compiler.