LEM-domain proteins share a folded structure, the 'LEM-domain', which binds a conserved chromatin protein named BAF. Most LEM-domain proteins are found at the nuclear membrane, but some are nucleoplasmic. All characterized members of this family bind nuclear lamin filaments. We summarize the 'founding' LEM-domain proteins LAP2, emerin and MAN1 ('SANE' or 'XMAN' in Xenopus) and their emerging roles in gene regulation and nuclear assembly. These roles are placed in the context of human diseases ('laminopathies') caused by mutations in either emerin or A-type lamins. Other LEM-domain proteins might modify the phenotype or severity of human laminopathy, or cause new laminopathies. We summarize evidence that the human genome encodes at least four additional LEM-domain proteins, designated Lem2 (NET-25), Lem3, Lem4 and Lem5. Early adaptation of a consistent nomenclature, such as the "Lem" names proposed here, will facilitate rapid progress in this field. Further investigation of 'founder' and novel members of this family will be important to understand nuclear structure, and presents new opportunities to understand human disease.