Proteins phase separate in the presence of synthetic polyelectrolytes as a consequence of electrostatic interactions. This phenomenon may form the basis of protein separations and has therefore been of technological interest. In this review, we consider previous reports of such phase separation, and attempt to describe the effects of various relevant factors, such as polymer MW, ionic strength, and macromolecular concentration. Models far protein-polyelectrolyte complexation are discussed. Current challenges and problems are noted.