The pharmaceutical and chemical industries depend on additives to protect enzymes and other proteins against stresses that accompany their manufacture, transport, and storage. Common stresses include vacuum-drying, freeze-thawing, and freeze-drying. The additives include sugars, compatible osmolytes, amino acids, synthetic polymers, and both globular and disordered proteins. Scores of studies have been published on protection, but the data have never been analyzed systematically. To spur efforts to understand the sources of protection and ultimately develop more effective formulations, we review ideas about the mechanisms of protection, survey the literature searching for patterns of protection, and then compare the ideas to the data.