In the study of thermoelectric materials, the elastic moduli are valuable for predicting and interpreting trends in lattice thermal conductivity and some aspects of electronic conductivity (e.g., electron-phonon interactions). Because elastic moduli are highly sensitive to the details of chemical bonding, they can also be used to detect subtle changes in crystal symmetry or site-disorder due to phase transitions. Consequently, measurements of elastic moduli are of fundamental value in the development of structure-property relationships in thermoelectric materials. However, experimental reports of the elastic constants of functional materials are relatively sparse, and temperature-dependent data is even less common. Further, unlike most types of functional materials, thermoelectric materials are used over an extremely wide temperature range (up to 1300 K in some cases). In our lab, we measure the elastic constants of polycrystalline and single crystalline thermoelectric materials across a wide temperature range (250–1300 K) using resonant ultrasound spectroscopy with Al2O3 buffer rods to separate the transducers from the hot zone. In this talk, I will discuss the high-temperature elastic properties of several classes of thermoelectric materials, including Mg3Sb2 and GeSe-AgBiSe2 alloys, emphasizing the role that such data can play in interpreting composition- and temperature-dependent trends in lattice thermal conductivity.