The chapter discusses the transport of proteins and nucleic acids into and out of the nucleus in eukaryotic cells. The nuclear envelope, a double membrane, separates the nucleus from the cytoplasm and contains nuclear pore complexes (NPCs) that allow passage of molecules. NPCs are large protein structures that regulate the flow of materials between the nucleus and the cytoplasm. The transport of molecules through NPCs is controlled by specific signals, such as nuclear localization signals (NLSs) and nuclear export signals (NESs), which bind to soluble carrier proteins. These carrier proteins, known as karyopherins, recognize and bind to NLSs or NESs, facilitating the translocation of proteins through the NPCs. The chapter also highlights the role of Ran GTPase in regulating the binding of cargo to karyopherins and the disassembly of complexes in the cytoplasm. Additionally, it discusses other carriers, such as TAP/Mex67 and calreticulin, which play roles in the transport of RNA and steroid receptors, respectively. The complexity of nuclear transport and the involvement of various cofactors and adapters are also explored, emphasizing the ongoing research to understand the mechanisms underlying this process.The chapter discusses the transport of proteins and nucleic acids into and out of the nucleus in eukaryotic cells. The nuclear envelope, a double membrane, separates the nucleus from the cytoplasm and contains nuclear pore complexes (NPCs) that allow passage of molecules. NPCs are large protein structures that regulate the flow of materials between the nucleus and the cytoplasm. The transport of molecules through NPCs is controlled by specific signals, such as nuclear localization signals (NLSs) and nuclear export signals (NESs), which bind to soluble carrier proteins. These carrier proteins, known as karyopherins, recognize and bind to NLSs or NESs, facilitating the translocation of proteins through the NPCs. The chapter also highlights the role of Ran GTPase in regulating the binding of cargo to karyopherins and the disassembly of complexes in the cytoplasm. Additionally, it discusses other carriers, such as TAP/Mex67 and calreticulin, which play roles in the transport of RNA and steroid receptors, respectively. The complexity of nuclear transport and the involvement of various cofactors and adapters are also explored, emphasizing the ongoing research to understand the mechanisms underlying this process.