Environmental temperature profoundly influences the body temperatures of reptiles, and hence the rates at which physiological processes occur. We review progress in understanding the thermal ecophysiology of New Zealand’s endemic, terrestrial reptiles (tuatara, geckos, and skinks), and in applying this knowledge to conservation. By understanding the constraints and opportunities that environmental temperature places on different life-history stages, including embryos in nests and those that develop within live-bearing females, we can plan better translocations, improve captive management, and make stronger predictions about risks from changes in climate. We encourage conservation physiologists to offer leadership in demonstrating the societal transformations necessary to sustain a liveable planet.