The importance of microscopic morphological control to metal electro-and electroless deposition in several emerging technologies is discussed. The use of in situ optical probes of the morphological development of deposits is described. A number of these are reviewed to describe both the potential of each method and the available literature on studies of electro-and electroless deposition. Included are optical probes of the mass transfer boundary layer, X-ray diffractive and spectroscopic methods, ellipsometry, surface-enhanced Raman spectroscopy, infrared absorption spectroscopy, second harmonic generation and electroreflectance.