Nuclear lamins are intermediate filament-type proteins that are the major building blocks of the nuclear lamina, a fibrous proteinaceous meshwork underlying the inner nuclear membrane. Lamins can also be localized in the nuclear interior, in a diffuse or spotted pattern. Nuclei assembled in vitro in the absence of lamins are fragile, indicating that lamins mechanically stabilize the cell nucleus. Available evidence also indicates a role for lamins in DNA replication, chromatin organization, spatial arrangement of nuclear pore complexes, nuclear growth, and anchorage of nuclear envelope proteins. In this review we summarize the current state of knowledge on the structure, assembly, and possible functional roles of nuclear lamins, emphasizing the information concerning the ability of nuclear lamins to self-assemble into distinct oligomers and polymers.