The natural resistance of proteins to crystallize is a major obstacle in molecular biology. Light scattering techniques can be employed to elucidate the mechanism(s) underlying the early nucleation stages in supersaturated protein solutions. In this work we review techniques and recent experiments from studies on supersaturated lysozyme solutions. The evidence corroborates that proteins crystallize via nucleation and spinodal decomposition mechanisms, well known from first-order phase transitions. At low volume fractions and due to non-specific protein-protein interactions, growth of fractal clusters (amorphous precipitate) accompanies nucleation. Aspects, associated with the experimental verification of these processes, the diificulties to predict the effective interaction potentials governing the process and possibilities towards diagnostic crystallization schemes are discussed.