Composites present a potentially cost-efficient and more durable alternative to the use of externally bonded steel plates for the rehabilitation and strengthening of concrete members, due to their high stiffness-to-weight and strength-to-weight ratios, corrosion resistance and overall ease of application in the field. Although a number of demonstration projects have shown the initial viability of such schemes, a number of critical questions still remain as related to short- and long-term durability as well as damage and failure mechanisms. In this paper a modified peel test is used to investigate the durability of the bond between concrete and composites under five different environmental exposure regimes. Two different epoxies were used with E-glass and carbon fibre reinforced composites. Differences in peel force and interfacial fracture energies based on material and environmental influences are discussed and modes of failure are presented.