The lipocalin family became established shortly after the structural similarity was noted between plasma retinol binding protein and the bovine milk protein, beta-lactoglobulin. During the past 60 years, beta-lactoglobulin has been studied by essentially every biochemical technique available and so there is a huge literature upon its properties. Despite all of these studies, no specific biological function has been ascribed definitively to the protein, although several possibilities have been suggested. During the processing of milk on an industrial scale, the unpredictable nature of the process has been put down to the presence of beta-lactoglobulin and certainly the whey protein has been implicated in the initiation of aggregation that leads to the fouling of heat exchangers. This short review of the properties of the protein will concentrate mainly on studies carried out under essentially physiological conditions and will review briefly some of the possible functions for the protein that have been described.