The molar heat capacity of copper has been measured between T = (6 and 400) K using an adiabatic calorimeter and thermometry calibrated on ITS-90. Our results are in good agreement with the measurements of Martin [Rev. Sci. Instrum. 58 (1987) 639] and Robie et al. [J. Res. US Geol. Survery 4 (1976) 631], made on the IPTS-68 temperature scale. The agreement is generally within 0.1% between 100 less than or equal to (T/K) less than or equal to 300 and increases to 0.5% below T = 100 K. However, when our results are compared to compilations of older data (taken before 1966), including the molar heat capacity values recommended by the CODATA Task Group on Thermophysical Properties, there are differences of up to 1% in the range 20 less than or equal to (T/K) less than or equal to 400. We concur with the conclusion of Martin that the CODATA results are in error below T = 300 K, and we conclude that the error extends to 400 K. The paper also includes a description of the instrumentation and procedures used to obtain the measurements in the Boerio-Goates laboratory. (C) 2004 Elsevier Ltd All rights reserved.