The GGA ((G) under bar olgi-localized, (gamma) under bar -ear containing, (A) under bar DP-ribosylation factor binding) family of multidomain coat proteins was first described in the year 2000. They are now known to occupy a central position in the trafficking of the mannose 6-phosphate receptors and other cargo molecules from the trans-Golgi network to the endosome/lysosome system. This review covers the recent structural and cell biological studies that have provided mechanistic insights into the function of the GGAs in mannose 6-phosphate receptor trafficking.