Protein–protein interactions (PPIs) refer to intentional physical contacts established between two or more proteins as a result of biochemical events and/or electrostatic forces. In fact, proteins are vital macromolecules, at both cellular and systemic levels, but they rarely act alone. Diverse essential molecular processes within a cell are carried out by molecular machines that are built from a large number of protein components organized by their PPIs. Indeed, these interactions are at the core of the entire interactomics system of any living cell and so, unsurprisingly, aberrant PPIs are on the basis of multiple diseases, such as Creutzfeld-Jacob, Alzheimer’s disease, and cancer. PPIs have been studied from different perspectives: biochemistry, quantum chemistry, molecular dynamics, signal transduction, among others. All this information enables the creation of large protein interaction networks – similar to metabolic or genetic/epigenetic networks – that empower the current knowledge on biochemical cascades and disease pathogenesis, as well as provide putative new therapeutic targets.