The constituent materials of fiber-reinforced polymer (FRP) composites include resins (matrix materials) and fibers (reinforcing materials). The fibers in the FRP composites may consist of carbon, aramid, glass, basalt, poly-p-phenylene-benzobisoxazole, or other types of polyethylene fibers. This chapter presents a comprehensive review of the basic mechanical properties and behaviors (e.g., tensile strength, stiffness, and strain capacity) of different types of continuous FRP sheets, based on the standard tensile test method. Moreover, the enhancement of their mechanical properties by adopting the concept of hybridization is also addressed. In addition, the effects of environmental conditions, such as low or high temperatures and freezing and thawing cycles, on the mechanical properties of FRP composites are analyzed and discussed. Furthermore, time-dependent behaviors, such as fatigue and creep behaviors, are comprehensively evaluated. Finally, the FRP bonding technique for concrete and steel structures, their installation procedure, and strengthening strategy are briefly described.