Protein–protein interactions (PPIs) are strongly predictive of functional relationships among proteins in virtually all processes that take place in the living cell. Therefore, the comprehensive exploration of interactome networks is one of the major goals in systems biology. The aim of Two Hybrid Technologies: Methods and Protocols is to provide a compendium of state-of-the art protocols for the investigation of binary PPIs with the classical yeast two-hybrid (Y2H) approach, Y2H variants and other in vivo methods for PPI mapping. Divided into two convenient sections, the first gives a survey of protocols that are currently employed for Y2H high-throughput screens by different expert labs in the field. Rather than detailing the principles of screening, which have been described previously, the focus is on different implementations of Y2H interactome mapping. The second section of the book considers innovative PPI detection methods that have the potential to emerge as alternative high-throughput methodologies. Written in the highly successful Methods in Molecular Biology™ series format, chapters contain introductions to their respective topics, lists of the necessary materials and reagents, step-by-step, readily reproducible laboratory protocols, and notes on troubleshooting and avoiding known pitfalls. Authoritative and accessible, Two Hybrid Technologies: Methods and Protocols  supplies researchers with a comprehensive toolbox for the identification of biologically relevant protein interactions.