Twenty years ago there was no known example in eukaryotes of a defined regulatory protein which bound to a specific DNA sequence in a target gene and regulated its expression. Since then a large number of such regulatory proteins, or transcription factors, have been defined and their roles in regulating the expression of specific genes analyzed. The aim of this work is to reproduce a series of key papers illustrating the increase of understanding of gene regulation. Each paper is followed by a commentary section which places the paper in context of what was known at the time and what has been established subsequently. This is designed to allow the student and the more experienced research worker to see how the field has developed over time and how the principles were elucidated. Because of its emphasis on the process of "scientific discovery", it should be of value to those working in various science fields as a student resource.