Proteins are the critical players in molecular recognition at the core of all biological processes. They can interact with the other components of cells, such as small-molecule metabolites, nucleic acids, membranes, and other proteins to build supramolecular assemblies and elaborate molecular machines that perform all sorts of functions, from chemical catalysis and mechanical work to signaling and regulation. As one of the most important interactions, Protein-Protein Interactions have been studied widely. So far large scale protein-protein interactions have been identified, and all the generated data collected together in specialized databases, enables the creation of large protein interaction networks.