The review considers the functions of the evolutionarily conserved nascent polypeptide-associated complex (NAC) and its subunits. NAC is a conserved heterodimeric protein detected in the genomes of all eukaryotes from yeast to human. NAC consists of α and β subunits, which form a dimer through their NAC domains association. NAC reversibly binds to the ribosome and contacts the nascent polypeptide to protect it from proteolysis and to facilitate its folding. Mutations and deletions of the NAC subunit-coding genes exert a lethal effect in early development of multicellular eukaryotes. NAC is involved in assembly and transport of proteins synthesized de novo and in ribosome biogenesis. A dimer of αNAC subunits binds to RNA and DNA and acts as a transcription factor. The β subunit interacts with caspase 3 and is possibly involved in apoptosis regulation. Heterodimeric NAC variants may be regarded as chaperones involved in the stress response of the cell and organism and as regulators of apoptosis. The β subunit-coding genes evolve rapidly, and their duplications may occur during evolution. These genes are expressed in a tissue-specific manner and code for subunits differing in the number of repetitive amino acid sequences identified as putative caspase-3 cleavage sites. NAC provides an example of a moonlighting protein, which performs many diverse biological functions.