Two new adaptor-related protein complexes, AP-3 and AP-4, have recently been identified, and both have been implicated in protein sorting at the trans-Golgi network (TGN) and/or endosomes. In addition, two families of monomeric proteins with adaptor-related domains, the GGAs and the stoned B family, have also been identified and shown to act at the TGN and plasma membrane, respectively. Together with the two conventional adaptors, AP-1 and AP-2, these proteins may act to direct different types of cargo proteins to different post-Golgi membrane compartments.