The sodium pump Na,K‐ATPase, located in the plasma membrane of all animal cells, is a member of a family of ion‐translocating ATPases that share highly homologous catalytic subunits. In this family, only Na,K‐ATPase has been established to be a heterodimer of catalytic (α) and glycoprotein (β) subunits. The β subunit has not been associated with the pump's transport or enzymatic activity, and its role in Na,K‐ATPase function has been, until recently, a puzzle. In this review we describe what is known about the structure of β and summarize evidence that expression of both a and β subunits is required for Na,K‐ATPase activity, that inhibition of glycosylation causes a decrease in accumulation of both α and β subunits, and we provide evidence that pretranslational up‐regulation of β alone can lead to increased abundance of sodium pumps. These findings are all consistent with the hypothesis that the β subunit regulates, through assembly of αβ heterodimers, the number of sodium pumps transported to the plasma membrane.— McDonough, A. A.; Geering, K.; Farley, R. A. The sodium pump needs its β subunit. FASEB J. 4: 1598‐1605; 1990.