This paper addresses the mechanics of adhesion, strengthening effect and durability issues of applications of CFRP composite materials in beams. The application of CFRP materials has been widely described, but the main focus has been on overall failure parameters. The first issue is strengthening capability of CFRP reinforcement for concrete beams. The second is the local interface bond stress-slip relationship, that is, the local t-slip. The last issue is the durability of the CFRP sheet/plate, when exposed to a hydro-thermal environment. The role of adhesion and the mechanics of concrete-CFRP adhesion and a sound understanding of the interface between the CFRP and concrete behavior is the key factor for controlling debonding failures in CFRP-strengthened RC beams.