Global warming affects livestock and especially poultry production, due to a higher variability of environmental conditions and average global temperatures, heat waves, risks for feed supply chains and sanitary issues. Considering chicken meat production that is still growing worldwide, high environmental temperatures decrease poultry growth performance and can even induce mortality. In this context innovative incubation programs were experimentally explored in order to improve the thermotolerance of broilers in the long term. They were aimed at re-introducing thermal variability during the embryogenesis of the bird, when its thermoregulatory system is still immature and plastic, in order to facilitate the later thermotolerance capacities of the bird. Cyclical increases in incubation temperatures, tested with different programs on slow growing birds in Africa, or fast-growing birds in Europe and Israel, have proved their efficacy to decrease mortality at slaughter age with very limited or no effects on performance. The biological basis of these improvements lies in long term physiological, metabolic and epigenetic changes in peripheral and/or central tissues controlling heat production, heat loss and stress response. Research in quails used as a model animal also showed that effects induced by changes in temperature during early incubation could be transferred to next generations with a partial reversibility of effects when the incubation treatment is not applied any more. The application of lower incubation temperatures during the late embryogenesis was also tested in fast growing broilers in order to improve cold tolerance, especially in chick when energy use and costs at start are high. This research could lead to applications in hatcheries for improving the adaptation of chickens in the long term to the foreseen increasingly varying environmental conditions.