In situ spectroscopic ellipsometry (SE) has been successfully used to accurately measure sputter deposition rates and optical constants of un-oxidized metal layers and to control the growth of magnetic multilayers. The structures include [Co/Cu](n), [Co/Au](n), [Co/Ni](n), [Co/Pd](n) and [Co/Pd/ Au](n). Layer thickness precision is better than +/-0.05 nm for layer thicknesses in the range of 0.2 nm to 10 nm. Closed-loop feedback control of layer thickness is also demonstrated. Good consistency was obtained by comparing the in situ SE results to x-ray diffraction measurements. Dynamic oxidation studies of [Co/Au](n) and [Co/Ni](n) multilayer structures are also presented.