The membrane phospholipid phosphatidylinositol is the precursor of a family of lipid second-messengers, known as phosphoinositides, which differ in the phosphorylation status of their inositol group. A major advance in understanding phosphoinositide signalling has been the identification of a number of highly conserved modular protein domains whose function appears to be to bind various phosphoinositides. Such 'cut and paste' modules are found in a diverse array of multidomain proteins and recruit their host protein to specific regions in cells via interactions with phosphoinositides. Here, with particular reference to proteins involved in membrane traffic pathways, we discuss recent advances in our understanding of phosphoinositide-binding domains.