In this paper, the durability of the adhesive bond between concrete and carbon fibre reinforced polymers (CFRP) strengthening systems has been investigated under accelerated ageing conditions, i.e., at 40°C and 95% relative humidity. Mechanical characterizations were carried-out on control and exposed CFRP strengthened concrete specimens, in order to assess the evolutions of the adhesive bond properties during hydrothermal ageing. Results from different experimental campaigns are presented and reveal significant evolutions (decrease in the adhesive bond strength and/or change in the failure mode) depending on various parameters, such as the surface preparation of concrete, the presence of a carbonated concrete layer, the nature of the CFRP overlay (carbon fibre sheets or pultruded CFRP plates), the ageing behaviour of the bulk epoxy adhesive itself, or the test configuration used to evaluate the adhesive bond strength (pull-off or shear loading test). Moisture diffusion from the superficial layer of concrete (i.e., diffusion of interstitial pore solution) towards the adhesive joint is suspected to be a key factor driving the degradation process during hydrothermal ageing.