In mammals, there are seven inositolphospholipids, collectively called phosphoinositides that serve as versatile molecules not only in receptor-mediated signal transduction but also in a variety of cellular events such as cytoskeletal reorganization, membrane trafficking, cell proliferation and cell death. Recent studies have revealed that the latter functions are mediated by direct interactions between phosphoinositides and proteins. Such proteins contain two types of phosphoinositide-binding regions; basic amino acid stretch and globular structural domain. Furthermore, spatially restricted compartment of phosphoinositides and their concentration are finely regulated by a large number of phosphoinositide kinases and -phosphatases, controlling localization-specific metabolism of this simple lipid whose aberrations cause various diseases such as cancer and diabetes.