Freezing point data for the system (ethylene glycol + water) were measured independently by two different laboratories. Measurements were made over the entire composition range with particular emphasis on mixtures containing from 55 to 85 weight percent ethylene glycol. Using time vs. temperature cooling and warming curves, the solid-liquid phase diagram of ethylene glycol and water mixtures was determined. The resulting phase diagram indicates the formation of a hydrate having a 1:1 molar composition (77.5 weight percent glycol). The data are compared with those reported previously in the literature and address the considerable disagreement between researchers for the 55 to 85 weight percent region.