This paper describes axial compression test results of 27 concrete cylinders confined by carbon fiber reinforced polymer composite jackets. The experimental parameters include plain concrete compressive strength and the thickness of the composite jacket. It is found that the carbon fiber composite jacketing can significantly increase the compressive strength and ductility of concrete. The test results indicate that concrete strength and confinement modulus, defined as the ratio of transverse confinement stress and transverse strain, are the most influential factors affecting the stress-strain behavior of confined concrete. The failure of the confined concrete was dominated by the rupture of the jacket at an average strain much smaller than the ultimate strain obtained from tension tests of flat coupons. In order to describe the main mechanical features of the confined concrete, a simple bilinear stress-strain model is suggested based on the theory of elasticity and minimum number of empirical equations determined from the tests. The simple model is shown to compare well with test results from previous studies by other researchers.