We report the observation of heavy-fermion superconductivity in CeCoIn5 at Tc = 2.3 K. When compared to the pressure-induced Tc of its cubic relative CeIn3 (Tc ∼ 200 mK), the Tc of CeCoIn5 is remarkably high. We suggest that this difference may arise from magnetically mediated superconductivity in the layered crystal structure of CeCoIn5.