The nuclear pore complex (NPC) is a structure that spans the nuclear envelope and provides a conduit between the nucleus and cytoplasm for the nucleocytoplasmic transport of macromolecules. The main components of the NPC are nucleoporins.  There are about 30 different nucleoporin proteins that have been identified and classified into 3 families: transmembrane nucleoporins, FG- or FN-nucleoporins, and WD-repeat seven-bladed propeller motif nucleoporins. Nucleoporins exists in a wide range of sizes and are named according to their molecular weight in kilodaltons. Nucleoporins appear to serve non-redundant functions in the NPC, however their roles in the NPC are not fully understood. Some have been shown to participate as essential structural elements that assemble into subcomplexes for the formation of an NPC with eight-fold symmetry.  Others have been suggested to play important roles in the active transport of macromolecules across the NPC; however none have been identified that exhibit motor or ATPase/GTPase activities.  Recent studies of leukemogenic fusion proteins that contain functional elements of nucleoporins have brought to light a possible novel function of nucleoporins in transcription. These findings illustrate that the functional roles of nucleoporins are likely to be expansive and varied, and much remains to be learned about the roles of the nucleoporins in NPC assembly, nucleocytoplasmic transport, and other cellular processes.