Basement membranes are sheet-like cell-adherent extracellular matrices that serve as cell substrata and solid-phase agonists, contributing to tissue organization, stability and differentiation. These matrices are assembled as polymers of laminins and type IV collagens that are tethered to nidogens and proteoglycans. They bind to cell surface molecules that include signal-transducing receptors such as the integrins and dystroglycan and form attachments to adjacent connective tissues. The cell receptors, in turn, provide links between the matrix and underlying cytoskeleton. Genetic diseases of basement membrane and associated components, collectively the basement membrane zone, disrupt the extracellular matrix and/or its linkages to affect nerve, muscle, skin, kidney and other tissues. These diseases can arise due to a loss of matrix integrity, adhesion strength and/or receptor-mediated signaling. An understanding of the mechanisms of basement membrane zone assembly and resulting structure can provide insights into the development of normal tissues and the pathogenic mechanisms that underlie diverse disorders.