Increasing device complexity and the need to achieve higher yields have created a need for a better understanding of growth processes and sample-driven growth control. Various optical probes are now available to meet these needs, including laser light scattering, surface photoabsorption, and reflectance-difference spectroscopy (RDS), and second-harmonic generation as well as refined versions of standard bulk-oriented approaches such as reflectometry and ellipsometry. I discuss basic challenges and approaches, then provide examples including the use of RDS to determine of surface reconstructions of (001) GaAs under atmospheric-pressure organometallic chemical vapor deposition, and the use of ellipsometry to achieve sample-driven closed-loop feedback control of AlxGa1-xAs layers of continuously graded compositions where the composition was determined by analysis of the outermost 3 Angstroms of depositing material.