The glass transition temperature, T_g, has a profound effect on many physical properties of polymeric conservation materials. It is at present difficult to find a reliable source of T_g data because a standard procedure for evaluating the raw analytical data is lacking. Moreover, comparison of T_g data taken from different sources is nearly impossible because the results can vary between analytical methods. In this study, a variety of conservation materials was analyzed by differential scanning calorimetry (DSC), and the T_g data were evaluated using the standard method established by the International Confederation for Thermal Analysis (ICTA). The complete set of data, appearing in the Conservation Information Network (CIN), can be used to aid conservators in selecting materials for a particular application.