The manufacture of optical coatings, computer disks, as well as advanced electronic multilayered devices and circuit structures requires high precision in the measurement and control of thicknesses and interfacial and surface roughnesses. Variable angle spectroscopic ellipsometry (VASE) is non-destructive and monolayer sensitive. VASE uses polarized light, and the technique can be applied in nearly any ambient, including air, vacuum, or corrosive environment. Applications to coated window glass, space protective coatings, semiconductor device, as well as sputtered media computer disk manufacturing are discussed. At the present time these NDE measurements are mainly ex situ, but in situ (during deposition) applications are being rapidly developed.