Hydrostatic pressure, as temperature, constitutes an efficient physical parameter to modify equilibrium and rate of biological processes. In this review, we will not present all the implications of high-pressure, but we will focus on proteins’ structural conformational modification, unfolding, oligomeric or protein aggregates dissociation and enzymatic activity. To this aim, some optical methods that were used in association with high-pressure to study protein structures (i.e. fourth derivative absorbance spectroscopy, fluorescence spectroscopy, infrared spectroscopy) and protein activities (kinetics measurements: stopped-flow and pressure jump methods) will be described in details. Some applications of these methods will be given including effects on proteins of food interest.