We present the results of tests measuring the life of carbon cold cathodes and determining what conditions limit the life of the cathode. Cathode life and stability are important for a broad range of applications, including displays, electron sources for satellite thrusters, x-ray tubes and microwave devices. Cathodes were tested in vacuum chambers using different gas environments as well as in sealed and gettered glass envelopes. We measured emission current half-lives of 10,000 - 20,000 hours or more in sealed display devices, depending on operating conditions. The presence of a significant oxygen or water partial pressure degrades the life of the cathode. After removing the gases the decay rate was restored to near the original value. A similar partial pressure of hydrogen gas has little or no effect on the life of the cathode. Initial results of operation in a xenon environment indicate carbon cold cathodes are much more robust compared to microtip cathodes. These results will be discussed with respect to the various applications considered for carbon cold cathodes.