Lamins are nuclear intermediate filament (IF) proteins. They assemble to fibrous structures that are positioned between the inner nuclear membrane and the peripheral chromatin. A small fraction of lamins is also present in the nucleoplasm. Lamins are required to maintain the nuclear structure and, together with their associated proteins, are involved in most nuclear activities. Mutations in lamins cause >14 distinct diseases, called laminopathies, that include heart, muscle, fat and early aging diseases. However, it is not clear how lamins are organized in vivo and how the disease mutations affect lamin organization and functions. Here, we will review structural aspects of lamin assembly, discuss differences between peripheral and nucleoplasmic lamins and describe the protein complexes that lamins form.