Metazoans have evolved several pathways to regulate the size of organs and ultimately that of organisms. One such pathway is known as Salvador-Warts-Hippo, or simply Hippo. Research on the Hippo pathway has grown exponentially during the past 8 years, revealing a complex signaling network. Intriguingly, within this complexity, there are levels of modularity. One level of modularity is represented by the unusually wide occurrence of the WW module in the Hippo core kinase cassette, the upstream regulatory components and the downstream nuclear proteins. We suggest that the prevalence of WW domain-mediated complexes in the Hippo pathway should facilitate its molecular analysis and aid prediction of new pathway components.