A number of full- and small-scale physical tests, and numerical studies examining the behaviour of thermally-activated piles have now been published. Collating studies involving monotonic and cyclic heating or cooling of isolated piles and pile groups, this article examines the reported results of the pile-soil interactions in terms of the pile head displacement and maximum internal stress changes during thermal loading, which are key for the design of thermally-activated piles. The results from the various studies largely confirm the complementarity of stress change and pile movement, and support the use of the bounds defined by a perfectly restrained pile and an unrestrained pile. The latter bound is unlikely to apply to all pile groups however, and more work is required in order to fully understand the limits of the former when applied to groups. Two aspects of cyclic thermal loading of T-A pile foundations have been highlighted; namely, that (i) once operational a T-A foundation will take some time to establish a new dynamic equilibrium reflecting the changing seasonal thermal boundary conditions and (ii) thermal ratcheting is most likely to occur when the pile shaft resistance is largely or fully mobilised by external loads, prior to thermal cycles being applied. It seems that these two effects are sometimes conflated and further investigation is needed in order to better understand their long-term effect. (C) 2018 Elsevier Ltd. All rights reserved.