The nuclear pore complex (NPC) creates an aqueous channel across the nuclear envelope through which macromolecular transport between nucleus and cytoplasm occurs. Nucleocytoplasmic traffic is bidirectional and involves diverse substrates, including protein and RNA. It is unclear whether import and export are mechanistically similar, but evidence suggests that numerous pathways may be involved. The discovery of filaments that extend out from each side of the NPC suggests that the NPC may also have a structural role, perhaps providing a connection between cytoskeletal elements of the nucleus and cytoplasm. If this suggestion is valid, it remains to be determined whether this aspect of NPC function is related to its role in nuclear transport. This review discusses recent developments regarding the structure of the NPC, characterization of its constituent proteins (nucleoporins), the mechanism by which transport occurs, the function of individual nucleoporins, and the pathway of NPC assembly and disassembly.