Book excerpt: This volume, part of the Advances in Molecular Biology series, presents work by pioneers in the field and is the first publication devoted solely to the yeast two-hybrid system. It includes detailed protocols, practical advice on troubleshooting, and suggestions for future development. In addition, it illustrates how to construct an activation domain hybrid library, how to identify mutations that disrupt an interaction, and how to use the system in mammalian cells. Many of the contributors have developed new applications and variations of the technique.