<p> This dissertation explores the effects of pressure and light on chalcogenide based materials. In ZnSe, ZnTe, and CdSe the surprising precipitation of the constituent anion under hydrostatic pressure and moderate laser exposure in high quality bulk and MBE film samples is explored in detail. In ZnSe the anomalous broadening in the TO(&Gamma;) phonon region is explored by careful low laser power pressure cycling experiments. The experimental results are supported with density functional theory calculations of the phonon band structure. Finally, the photo-induced crystallization onset of amorphous selenium films is explored as a function of temperature and substrate structure. The morphology of the photocrystallized spots is also explored using Raman mapping, optical microscopy, and atomic force microscopy.</p>