Fiber-reinforced polymer (FRP) sheets have been increasingly used to reinforce and repair tunnel linings and the slabs of viaducts owing to their advantages. In these FRP-strengthened structures, both in-plane shear stress and out-of-plane normal stress are imposed on the interface between the FRP sheets and concrete. Concrete spalls from the concrete surface owing to different failure mechanisms. To study the bonding and debonding mechanism behind spalling failure, a punching–peeling test against the spalling of concrete pieces is an important tool. In this chapter, the peeling behavior and the spalling resistance of FRP sheets externally bonded to concrete plates and beams are introduced, based on available experimental and analytical investigations. An extremely useful analytical technique for this problem is also introduced in this chapter.