The transport of histones from the cytoplasm to the nucleus of the cell, through 
the nuclear membrane, is a cellular process that regulates the supply of new 
histones in the nucleus and is key for DNA replication and transcription. 
Nuclear import of histones is mediated by proteins of the karyopherin family of 
nuclear transport receptors. Karyopherins recognize their cargos through linear 
motifs known as nuclear localization/export sequences or through folded domains 
in the cargos. Karyopherins interact with nucleoporins, proteins that form the 
nuclear pore complex, to promote the translocation of their cargos into the 
nucleus. When binding to histones, karyopherins not only function as nuclear 
import receptors but also as chaperones, protecting histones from non-specific 
interactions in the cytoplasm, in the nuclear pore and possibly in the nucleus. 
Studies have also suggested that karyopherins might participate in histones 
deposition into nucleosomes. In this review we describe structural and 
biochemical studies from the last two decades on how karyopherins recognize and 
transport the core histone proteins H3, H4, H2A and H2B and the linker histone 
H1 from the cytoplasm to the nucleus, which karyopherin is the major nuclear 
import receptor for each of these histones, the oligomeric state of histones 
during nuclear import and the roles of post-translational modifications, 
histone-chaperones and RanGTP in regulating these nuclear import pathways.