Differential thermal analysis (DTA) has been applied to the examination of a variety of glasses and glass-glass reactions. The method is described and results that were obtained which illustrate the usefulness of the technique are shown. Reversible and nonreversible latent heat anomalies have been observed in glass which are believed coincident with the glass transition, phase separation, devitrification processes, and dissolution of crystalline phases. The heat effect believed to be associated with the glass transition is reproducible, reversible and different for different glasses, and is observed as an endotherm on heating and an exotherm upon cooling. The change in the thermal glass transition temperature (Tt) as a function of composition was found to be sensitive to within approximately a 1% variation of one of the constituents of the glass enabling the determination of a "glass transition phase diagram" for two interacting glasses. The technique has shown itself to be a useful tool in quality control of raw glasses and in monitoring glass forming processes. © 1975 American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc.