How are proteins or RNA-protein complexes imported into the nucleus or exported from the nucleus into the cytoplasm? What is the function of soluble factors in different transport pathways? How do transport receptors interact with their substrates? What is the role of nucleoporins, components of the nuclear pore complex, in import and export of distinct transport cargos? How do proteins reach the inner nuclear membrane? To address these questions, we are using several biochemical and cell biological techniques to follow and to visualize nuclear transport of soluble proteins as well as of membrane proteins.