Book excerpt: New genomic information has revealed the crucial role that protein–protein interactions (PPIs) play in regulating numerous cellular functions. Aberrant forms of these interactions are common in numerous diseases and thus PPIs have emerged as a vast class of critical drug targets. Despite the importance of PPIs in biology, it has been extremely challenging to convert targets into therapeutics and targeting PPIs had long been considered a very difficult task. However, over the past decade the field has advanced with increasing growth in the number of successful PPI regulators. Protein–Protein Interaction Regulators surveys the latest advances in the structural understanding of PPIs as well as recent developments in modulator discovery.